Obisium Illiger, 1798

Judson, Mark L. I., 2012, Nomenclatural problems associated with the generic names Obisium Leach, 1814, Blothrus Schiödte, 1847 and Neobisium Chamberlin, 1930 (Arachnida: Chelonethi), Zootaxa 3475, pp. 21-35 : 23-25

Obisium Illiger, 1798 and Obisium Leach, 1814 as distinct nominal taxa

Obisium was first employed as a name for a different nominal taxon to that of Illiger (1798) by Leach in the “Crustaceology” section of the Edinburgh Encyclopaedia, which was divided between parts I (1813, pp. 383–384), and II (1814, pp. 385–437) of volume 7 ( Sherborn 1937). Authorship of this section was not explicitly indicated, but later authors, notably Leach himself (e.g. Leach 1817, p. 57; Leach 1819) attribute it solely to W.E. Leach. While it is clear that Leach provided most of the scientific content, for which he had been commissioned ( Harrison & Smith 2008), the final form was the responsibility of the editor, D. Brewster, who did not always follow Leach’s classification. This explains why there are frequent references to “Leach’s MSS”, which has been a cause of confusion in the past. Stebbing (1897) was bemused by a similar case (the introduction of Nephrops Leach, 1814 in the synonymy of Astacus Fabricius, 1775 ) and noted that Leach had introduced this generic name “as if it were that of a stranger”, which led him to make the rather implausible suggestion that “the contumely and struggle for existence to which many of his now accepted genera were in their earlier days exposed may explain his reluctance in this instance to do what he thought right.” In order to conform to previous usage (including numerous decisions of the ICZN (e.g. International Commission on Zoological Nomenclature 1956, Direction 37, pp. 57 and 73), Leach is here treated as the sole author of the Crustaceology section in the Edinburgh Encyclopaedia, but it must be borne in mind that some parts of the text were written by the editor, D. Brewster. In this work, Obisium Illiger, 1798 is listed (p. 429) as a synonym of Chelifer Geoffroy, 1762 , which is divided into two unnamed groups, the first containing Chelifer cancroides (Linnaeus, 1758) and C. cimicoides (Fabricius, 1793) , and the second containing Chelifer trombidioides Latreille, 1804 [misspelt “ trombidioidos ” by Brewster in the heading; correctly spelt trombidioides by Leach in its synonymy]. However, the new combination Obisium trombidioides (Latreille, 1804) is introduced in the synonymy of Chelifer trombidioides and attributed to Leach in the form “Leach’s MSS”. Also cited in the synonymy of C. trombidioides is the “ Pince ischnochéle Hermann” [a misprint for ischnochèle], which is the vernacular name used by Hermann (1804) for Chelifer ischnocheles Hermann, 1804 . In the comments that follow the classification, Brewster adds that

“These two divisions of the genus certainly have distinct characters enough to form two genera; we therefore, perhaps, should follow Mr Leach1, who proposes to call the first division CHELIFER , a name first given by Geoffroy; the second OBISIUM , a name proposed by Illiger for the genus as it now stands [i.e. Chelifer sensu lato].”

Thus Obisium is being used in two different senses: Brewster is using it in Illiger’s sense as a synonym of Chelifer , whereas Leach is applying it to a different taxonomic concept, containing only Chelifer trombidioides Latreille, 1804 . This is a deliberate action on Leach’s part and not a lapsus, because the two species originally placed in Obisium Illiger, 1798 are excluded from Obisium sensu Leach. Thus a new genus, Obisium Leach, 1814 is proposed, for which the type is Chelifer trombidioides by monotypy (Articles 67.12, 68.3). Rather than coin a new name for the new genus, Leach chose to adopt one that had already appeared in the literature and, in so doing, effectively created a junior homonym— Obisium Leach, 1814 —of Obisium Illiger, 1798 . The fact that Brewster in Leach (1814) treated Obisium sensu Leach (1814) as a junior subjective synonym of Chelifer (by assigning C. trombidioides to the latter genus) does not affect its availability because Obisium Leach, 1814 has been treated as an available name (albeit incorrectly attributed to Leach, 1815 or Leach, 1817) before 1961 (Article 11.6.1). Examples include Simon (1879), Kew (1911), Chamberlin (1930) and Beier (1932), with the latter referring to “ Obisium (non O., Illiger 1798) Leach 1817 ”.

It is unfortunate that Obisium Leach, 1814 should have been proposed in such a confusing way. Leach’s intentions were made clearer in a paper read at meetings the Linnean Society of London in 1814 and published as Leach (1816a), in which Chelifer Geoffroy, 1762 and Obisium Leach, 1814 were treated as separate genera, with Obisium trombidioides (Latreille, 1804) being the only species included in the latter. Leach (1816a, p. 391) wrote “ OBISIUM, Illig. ”, but, as in his other works, this is more a bibliographic reference than an indication of authorship in the modern sense of the Code (on the following page, for example, he refers to “ Scorpio, Latr., Fabr. &c.”). The same arrangement was also presented by Leach (1816b, p. 433) in the Supplement to the Encyclopaedia Britannica, which includes a figure (pl. XXIII, fig. 5) of O. trombidioides that clearly represents a species of the genus

1. Leach was awarded a medical doctorate from St Andrews University on 13 January 1812, at the age of 20 ( Harrison & Smith, 2008). Either Brewster was unaware of this or he had received Leach’s manuscript prior to this date.

Chthonius C.L. Koch, 1843 (Chthoniidae) , as previously noted by Kew (1916). The only species of Chthonius present in the W.E. Leach collection (conserved in the Natural History Museum, London) is C. ischnocheles ( Hermann, 1804) ( Judson 1997) , which is currently considered to be a senior subjective synonym of C. trombidioides .

The idea that Obisium Illiger, 1794 and Obisium Leach, 1814 can be treated as separate nominal taxa has generally met with scepticism in discussions of this case with colleagues. Although the Code can only apply to actions in their published form, without recourse to speculation on the motivations behind them, it may be instructive to consider another example in which Leach took an existing name in a group and applied it to a different genus of the same group. Kugelann (1794, pp. 580–581) proposed the generic name Bryaxis Kugelann, 1794 for a single species, Bryaxis schneideri Kugelann, 1794 , of the beetle subfamily Pselaphinae (Insecta, Coleoptera , Staphylinidae ). Leach (1817, p. 85) subsequently used the same name for a different genus of Pselaphinae , containing seven species, but not B. schneideri . Besuchet (1969) suggested that Leach (1817) was “probably unaware of the work of Kugelann”, but Leach must have consulted the work of Kugelann & Illiger (1798), which contains a diagnosis of the genus (p. 293), as well as that of Latreille (1804b), which mentions “le bryaxis de Kugelann” (p. 358). Leach (1817) may also have seen Kugelann (1794), since he treats Hydraena Kugelann, 1794 (Insecta, Coleoptera , Hydraenidae ) as a valid genus, although he misspelt the author’s name as “Kugellan”. Thereafter, Bryaxis Kugelann, 1794 and Bryaxis Leach, 1817 were treated as separate nominal taxa by coleopterists, as well as by the ICZN when it placed Bryaxis Leach, 1817 on the Official Index of Rejected and Invalid Names in Zoology in Opinion 887 (International Commission on Zoological Nomenclature 1969) as a junior homonym of Bryaxis Kugelann, 1794 .

While it may seem hard to comprehend now, the practice of re-utilising a synonymous name in a different sense was not exceptional in Leach’s time. Indeed, Leach was following the most widely accepted rules of nomenclature then available, namely those of Linnaeus’ (1751) Philosophia botanica, which had been adapted for arthropods by Fabricius (1778) in his Philosophia entomologica. Aphorism 244 of Linnaeus (1751, pp. 196–197) reads:

Nomina Generica, quamdiu Synonyma digna in promtu sunt, nova non effigenda.

Novis e. c. detectis Generibus nova nomina aptissime conficiuntur & iisdem imponuntur.

Antiquum si dirimatur genus in plura, confultum eft nova non effingere nomina generica, quamdiu digna in phalange synonymorum specierum supersint.

[New generic names ought not to be made, so long as there are any of the synonymous names that deserve to be retained. When new genera are discovered, new names ought to be given them; but if an ancient genus must be divided into two or more, it is proper not to coin new generic names, so long as there are any of the synonymous names belonging to any of the species of that genus, worthy to be retained. Translation by Rose (1775, p. 298).]

Leach was evidently following this rule when he divided Chelifer into two genera and used the name Obisium for the ‘new’ genus. Thus Obisium in Leach’s sense is a different taxon to that of Illiger (1798). This situation corresponds to that of metomonymy, as recently characterised by Dubois (2012), who gives a number of examples. It might be countered that Leach had not divided the ‘ancient’ Chelifer because C. trombidioides was unknown to Illiger. It is unlikely that Linnaeus intended such a strict interpretation of the original genus, but even then Leach’s action would be allowed by aphorism 245:

“ Nomen genericum unius generis, nisi supervacaneum, in aluid transferri non debet, licet eidem aptius competeret. ” [“The generic name of one genus, unless it be superfluous, ought not to be transferred or given to another genus, though it would suit it better”. Translation by Rose (1775, p. 299).]

Obisium , as a replacement for Chelifer , was clearly a superfluous name, allowing Leach to apply it to a different genus, in the same way that Linnaeus had done on a number of occasions for plant genera ( Gray 1847). This practice was, however, contested by others, including Westwood (1836), who considered Leach’s use of the name Obisium to be ‘improper’. The “re-issuing” of names in this way was rejected in the nomenclatural rules proposed by Strickland et al. (1843), but they still allowed names that had previously been so adopted, writing “These discarded names may however be tolerated, if they have been afterwards proposed in a totally new sense, though we trust that in future no one will knowingly apply an old name, whether now adopted or not, to a new genus” (footnote, p. 264; Italics in original). However, it was not until the publication of the first international code of nomenclature (International Commission on Zoological Nomenclature 1905) that such usage was formally proscribed.

Of course, the current rules apply retroactively to such cases and the fact that Leach’s actions were justifiable at the time they were made does not mean that they remain valid now. Nevertheless, it is important to understand Leach’s motives in order to show that Obisium Leach, 1814 can be treated as an available name. If, as Harvey & Mahnert’s (2011) interpretation implies, Leach’s usage had been some sort of aberration, no new taxon would be involved and Obisium Leach, 1814 would never have existed, whereas when it is accepted that Leach deliberately separated Obisium as a new nominal taxon, there is nothing to prevent this being treated as an available name, completely independent of the homonymous genus Obisium Illiger, 1798 . This, as we shall see, removes some nomenclatural problems that Harvey & Mahnert (2011) did not anticipate when treating Cheliferidae and Obisiidae as objective synonyms, but it also leads to the recognition of serious problems arising from the fact that C. trombidioides is the type species of Obisium Leach, 1814 .