RHYNCHONELLID^. 



151 



umbone of the opposite valve. Dorsal valve rather more convex than the ventral, with 

 a broad fold, which, commencing at the front margin, extends to a short distance only, 

 and dies out. In some specimens three or four romided ribs occupy the fold, the lateral 

 portions of the valve remaining smooth ; while, again, in other examples, two or three 

 ribs exist also close to the margin, as seen in the ventral valve. Inside the ventral 

 valve, a short septum supports a small V-shaped chamber, formed by the converging 

 dental plates. Two specimens measured — 



Length 7, width 7^, depth 5 lines. 

 „ 10, „ 10, „ 6 „ 



Ods. It is with considerable hesitation that I place this species in the genus Fenta- 

 merus, as I am imperfectly acquainted with its internal characters ; but Mr. Salter tells 

 me it has a good septum and V-shaped chamber. The lines observable on the surface 

 of some specimens, and an internal cast in the collection of Sir R. Griffith, described in 

 the * Synopsis of Irish Sil. Fossils' by M'Coy as Atrypa rotundata (fig. 12 of my plate), 

 lead me to beheve it is a true Pentamerus. This fossil appears to vary to some extent 

 in the presence or absence of ribs on the lateral portions of the valves. The beaks are 

 also very approximate. 



Position and Locality. Murchison's original example, which can be seen in the 

 Museum of the Geological Society, was found in the Wenloch limestone of Wenlock Edge. 

 ^ It occurs also in the Woolhope limestone of the Malvern district less rarely. Prof. M'Coy 

 mentions it from sandstone at Alt Goch, Llanfyllin, Montgomeryshire (but no such 

 specimen is in the Cambridge Museum; and it is probably a mistake). The Irish 

 specimen described by M'Coy is from Kilbride, Cong, Co. Galway, in May Hill sand- 

 stone, or Upper Llandovery rock. 



Pentamerus oblongus, J. de C. Sow. PI. XVIII, figs. 1—12; PI. XIX, figs. 1, 2. 



Pentamerus l^vis, Sow. Min. Con., vol. i, p. 76, pi. xxviii, June or August, 1813. 



— OBLONGUS, J. de C. Sow. Sil. Syst., pi. xix, fig. 10 (not fig. 12), 1839. 



— L^vis, Sow. Sil. Syst., pi. xix, fig. 9, 1839. 



— OBLONGUS, Hall. Geol. Report New York, p. 7, figs. 1 — 5, 1843. 



— — M'Coy. Synop. Sil. Foss. Ireland, p. 38, 1846. 



— — De Fern. Bull. Soc. Geol. France, 2nd ser., vol. iv, p. 690, 



1847. 



— L^vis, Phillips and Salter. Mem. Geol. Surv., vol. ii, part 1, p. 292, 



1848. 



— OBLONGUS, Bronn. Index Pal., p. 945, 1848. 



— — et -LJEVis, D'Orb. Prodrome, vol. i, p. 20, 1849. 



— — Salter. Journ. Geol. Soc, vol. vii, pp. 171, 172, 1851. 



— — Hall. Pal. New York, vol. ii, p. 79, pi. xxv, fig. 1, and pi. 



xxvi, fig. 1, 1852. 



