Viaphacops venezuelensis, 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

Viaphacops venezuelensis , new species

Figure 3 , A–D

DIAGNOSIS: Cephalon broader than long, with posterior border slightly concave. Composite glabellar lobe short and broad, round­ ed anteriorly, flattened dorsally, with moderate inclination anteriorly. Glabellar surface ornamentated with low, rounded tubercles, each one somewhat separated from the others, and gradually diminishing in size anteriorly. Occipital ring without spines or tubercles. Genal angles rounded. Eyes with 13 or 14 dorsoventral files, with 3 or 4 lenses per file. Visual surface convex, raised somewhat above glabellar level.

HOLOTYPE: MBLUZ P­33 , cephalon (represented by an internal mold), from upper level of the Caño del Oeste Formation , Perijá Mountains, NW Venezuela. Cast of holotype AMNH 46578 .

ETYMOLOGY: Named after Venezuela, the country of origin.

AGE: Middle Devonian (Eifelian/Givetian).

DESCRIPTION: The cephalon is approximately twice as broad as long, with a maximum cephalic width of 34 mm (adjacent to genal angles), and a maximum length of 16 mm (sagittally from front of glabella to posterior margin of occipital ring). Dorsally the glabella is moderately inflated, flattened, and inclined forward, and anteriorly its frontal surface is vertical. The length (sag.) of the composite glabellar lobe is 12 mm (formed by the union of the anterior, third, second, and medial portion of the first glabellar lobes; Eldredge, 1973: 316). The composite glabellar lobe is covered by low, rounded tubercles, each one somewhat separated from the others and diminishing gradually in size toward the anterior region of the glabella. Tubercles are not present on the occipital ring or genae. The maximum anterior glabellar width at the intersection of the axial furrows and anterior cephalic margin equal 20 mm. The posterior glabellar width is 10 mm. The axial furrows are straight, broad, deep, and strongly divergent anteriorly. The second and third glabellar furrows are shallow, almost indistinct. A deep, broad transglabellar furrow is apparently formed by confluence of the occipital furrow (S0) and first pair of glabellar furrows (S1). All the paired glabellar lobes are incorporated into the composite glabellar lobe. The distal portion of the first glabellar lobe (L1) forms a pair of lateral preoccipital lobes. The visual surface is supported by an eye socle, elevating the eye somewhat above the level of the glabella. The palpebral lobes are well developed but are not so high as the visual surface. The eyes have 13 or 14 dorsoventral files on the visual surface (the posteriormost files are somewhat indistinct, but there are certainly no more than 14 files). In each file the number of lenses is no more than four lenses per file (in the anteriormost two files there are only two or three lenses). The genae are almost vertical and extend posteriorly behind the occipital ring. The genal angles are rounded. The occipital ring is narrow (long.), without ornamentation or spine, slightly curved anteriorly (sag.), slightly above the glabellar lobe, with a width of 10 mm. The posterior margin of the cephalon and the occipital ring are both raised to form a prominent margin.

The thorax and pygidium are unknown.

Figures

Fig. 3. Viaphacops venezuelensis, n. sp., holotype, MBLUZ P­33, internal mold of cephalon. (A) Dorsal view; (B) frontal view; (C) lateral view; (D) oblique dorsolateral view of right side.