Malletiidae H. Adams

Hryniewicz, Krzysztof, Little, Crispin T. S. & Nakrem, Hans Arne, 2014, Bivalves from the latest Jurassic-earliest Cretaceous hydrocarbon seep carbonates from central Spitsbergen, Svalbard, Zootaxa 3859 (1), pp. 1-66 : 16

Family Malletiidae H. Adams & A. Adams, 1858

Genus Mesosaccella Chavan, 1946

Type species. Nucula foersteri Müller, 1847

Remarks. The genus Mesosaccella is probably a bucket taxon, as it contains species with a wide range of external morphological features. This diversity is encapsulated into three morphogroups. The first comprises roughly oval, variably elongated and non-carinate species with ornament composed only of growth lines, including M. elliptica ( Goldfuss, 1837) from the Rhaetian–Pliensbachian of Europe ( Palmer 1973; Hodges 2000), M. morrisi ( Deshayes, 1853) from the Callovian of England and France ( Duff 1978) and M. choroschovensis ( Borissjak, 1904) from the Volgian of Russia and Greenland ( Borissjak 1904; Fürsich 1982). The second Mesosaccella morphogroup comprises elongated species with slightly pointed posteriors, external ornament of growth lines, with or without weak commarginal ridges, and growth line deflections on the posterior parts of the shell. This group includes our M. rogovi sp. nov., M. grovei ( Lartet, 1872) and M. larteti Chavan, 1947 , from the Campanian of Palestine ( Chavan 1947), as well as species currently classified within other genera, but also fitting the definition of Mesosaccella , such as Leda striatula Forbes, 1845 , from the Cretaceous of India ( Forbes 1845, p. 148, pl. XVII, fig. 14). The third Mesosaccella morphogroup comprises short and inflated forms with pointed posteriors, strong commarginal ornament fading on the anterior and posterior parts of the shell and carination of the posterior shell area. This group includes our M. toddi sp. nov., and species described as Nuculana speetoniensis Woods, 1899 , and Nuculana lineata J. de C. Sowerby, 1836 , by Woods (1899).