Rhenops odremani, DE CARVALHO & MOODY, 2000

DE CARVALHO, MARIA DA GLORIA PIRES & MOODY, JOHN, 2000, A Middle Devonian Trilobite Assemblage from Venezuela, American Museum Novitates 3292, pp. 1-15 : 1-15

Rhenops odremani , new species

Figures 4 , A–F; 5 A, B

Rhenops , n. sp., Lieberman and Kloc, 1997: 76, fig. 15, 1–8.

DIAGNOSIS: Cephalon relatively elongate in outline, ogival, with anterior cephalic border slightly pointed medially; S3 faintly sinusoidal, glabellar lobes not inflated; genal spines long and broad, slightly curved at their extremities, with a ridge on the dorsal surface extending from the cephalic posterior border to the tip. Eyes above glabellar level with maximum of seven lenses per dorsoventral file.

HOLOTYPE: MBLUZ P­987 , external mold of cephalon lacking the left genal spine, plus parts of first three thoracic segments. Cast of holotype AMNH 46579 . Dimensions of the holotype: cephalic length (sag.) approximately 12.6 mm from occipital furrow to anterior margin of cephalon; width approximately 22.2 mm across posterior margin of cephalon.

PARATYPES: MBLUZ P­985 , internal mold of pygidium; MBLUZ P­986 , internal mold of cephalon with part of the right genal spine, plus first three thoracic segments; MBLUZ P­1079 , small enrolled specimen with the pygidium preserved (not figured). Casts of paratypes AMNH 46580 , 46581 , 46582 . All material of Rhenops odremani n. sp. is housed in the Museo de Biología, Universidad de Zulia ( MBLUZ), Maracaibo, Venezuela, not in the Department of Geology , University of Rio de Janeiro, Brazil, as was stated by Lieberman and Kloc (1997: 77). Catalog numbers for the specimens illustrat­ ed in Lieberman and Kloc (1997: fig. 15) are as follows: Nos. 1, 2 = MBLUZ P­1079 ; Nos. 3–6 = MBLUZ P­986 ; Nos. 7, 8 = MBLUZ P­985 .

ETYMOLOGY: Named for Oscar Odreman, who has made significant contributions to the paleontology of Venezuela.

PROVENANCE AND AGE: Caño del Oeste Formation, Middle Devonian (Eifelian/Givetian), Perijá Mountains, NW Venezuela.

DESCRIPTION: The cephalon has a relatively elongate outline, tapering anteriorly, and thus resembles a gothic arch (ogival shape), with the anterior cephalic border slightly pointed medially. The cephalic profile is moderately convex. Axial furrows are narrow, well impressed, subparallel to S1 then becoming divergent anteriorly. Glabellar furrows are weakly impressed and moderately wide. S1 is roughly crescent­shaped and deeper adaxially; S2 is transverse, narrower than S1; S3 is faintly sinusoidal. Lateral glabellar lobes (L1–L3) are flat sagittally. The first pair of lateral glabellar lobes (L1) is somewhat flexed forward, giving the appearance of a transglabellar lobe; L2 is approximately rectangular and smaller than L3, which has a wedge shape. The frontal glabellar lobe is strongly expanded anteriorly and laterally, with its margin smoothly rounded in dorsal view, sloping gently anteriorly and laterally. The cephalic lateral border furrow is not discernible; the cephalic posterior border furrow is deep and flexed forward medially. The eyes are large and raised above the glabella, occupying about 50% of glabellar length, and are positioned proximally and posteriorly on the cephalon. Each eye is in contact with the anterolateral corner of L3 anteriorly, and posteriorly is located a short distance from the axial furrow. The posterior edge of the visual surface is situated posteriorly to a transverse line tangent to the anterior edge of the occipital ring. The visual surface has a maximum of seven lenses per dorsoventral file. The palpebral region of the fixigena slopes toward the glabella. Genal spines are relatively long and broad, curved at their extremities, with a ridge on the dorsal surface extending from the cephalic posterior border furrow to the tip. The internal margins of the genal spines are not parallel to the sagittal line, but are deflected posteriorly at an angle of approximately 15°. The length of the genal spine cannot be determined accurately in any of the available specimens; it has approximately the same length as the rest of the cephalon. The occipital ring is not well preserved in the material and its morphology cannot be determined. The preserved surface of the cephalon is rough and has a granular appearance in places. In epoxy casts the surface appears to be tuberculose (fig. 4B), but this is an artifact of the casting medium. We have not found convincing evidence that tubercles are present on the original specimen.

The pygidium is lacking in the holotype of Rhenops odremani , new species, but is pres­ ent in two of the paratypes ( MBLUZ P­985 and MBLUZ P­1079 ). The following description is based mainly on MBLUZ P­985 as the pygidium is better preserved than in MBLUZ P­1079 . The pygidium is small and subelliptical in outline; in MBLUZ P­985 it has a total length of approximately 5.6 mm (sag.) and maximum width about 9.6 mm (its anteriormost region). In lateral view the posteriormost region of the axis slopes to the rear. The axis is slightly raised above the pleural field, and includes at least 10 rings. The first seven rings are easily distinguished, but the remainder become progressively obsolete posteriorly and cannot be accurately counted. The anterior margins of the first five rings are slightly arched anteriorly; after the fifth ring they are straight. The axis tapers posteriorly as far as the fifth ring, after which the axial furrows are roughly parallel back to the terminus of the axis. The pleural region consists of five pairs of pleurae of approximately equal width, and with equally elevat­ ed anterior and posterior pleural bands; the pleural furrows are deeper than the interpleural furrows. The first three pleurae are gently curved posteriorly, and the last two are curved more abruptly. The fifth pleura is much shorter than the others and it is very close to the pygidial axis. Each pleura terminates with a long, broad, and flat lappet, but its distal tips are not well preserved. The external lateral margin of each lappet is smoothly curved and the inner margin is approximately straight. The terminal lappet is slightly broader than the posterior part of the axis, but its terminal part is missing. No ornamentation is present on the pleurae or pygidial axial rings. The only ornamentation observed in these specimens is fine granulation on the lappets, but other details are difficult to ascertain as both the available pygidia are weathered .

Figures

Fig. 4. Rhenops odremani, n. sp. (A–C) Cast made from holotype (an external mold), MBLUZ P­ 987, in (A) dorsal view; (B) frontal view; (C) lateral view; (D­F) Paratype, MBLUZ P­986; internal mold of cephalon in (D) dorsal view; (E) frontal view; (F) lateral view.

Fig. 5. (A, B) Rhenops odremani, n. sp. Paratype, MBLUZ P­985; internal mold of pygidium. (A) dorsal view; (B) lateral view. (C­E) Greenops perijaensis, n. sp., latex cast of external mold in the holotype, MBLUZ P­1448. (C) Dorsal view; (D) frontal view; (E) lateral view.