﻿PENTAMERUS. 



73 



Stringocephalus brevirostris belonged to the genus Pcntamcrus, but one of the most 

 remarkable features of this curious species is that, in certain individuals, both valves are 

 almost equally and evenly convex (figs. 7, 10, 11), and in this shape they would constitute 

 Phillips's so-termed Ter. cassidea, but not the species so named by Dalman. In some 

 examples, such as in fig. 9, there exists a slightly raised mesial fold in the dorsal valve, 

 but which in other examples is replaced by a depression or sinus of greater or lesser depth 

 (figs. 1, 5, 6), and I believe that such examples as fig. 1 have been termed Pent, globus by 

 Bronn and Sandberger. Another peculiarity consists in the presence or absence of 

 longitudinal ribs in the sinus of the dorsal valve, or on the fold of the ventral one. The 

 specimen fig. 5, for instance, has no ribs in either valve, while these are present in such 

 specimens as fig. 4, and indeed, had space permitted, we could have given drawings of 

 every stage or passage in shape uniting the extreme conditions above described. 



Pentamerus brevirostris occurs plentifully in the Middle Devonian limestone of 

 Woolborough quarry, near Newton Abbot; near Chircombe Bridge, West Ogwell, 

 and Bradley, North Devon ; Barton, Lummaton, and Hope's Nose, near Torquay ; at 

 Dartington, near Totness ; and, according to Professor M'Coy, at Plymouth in 

 Devonshire. On the Continent it has been found in the Eifel, and Nassau, also at 

 Ferques in the Boulonnais, and in several other Devonian localities. 



Pentamerus biplicatus, Schnur. PI. XIV, figs. 31, 32. 



Pentamerus biplicatus, Schnur. Programni der vereinigten lidhern Burger und 



Provinzial-Gewerbeschule zu Trier fur das Schuljahr., 

 p. 8, 1851 ; and in Dunker und von Meyer's Palseonto- 

 graphica, vol. iii, p. 196, pi. xxxi, fig. 3, 1853. 



Spec. Char. Pentagonal, transverse or slightly elongated, globose. Dorsal valve 

 evenly convex to within a short distance of the front, where a shallow sinus is produced 

 with a small rib in its centre. Ventral valve deeper and more convex than the opposite 

 one, with a short biplicated fold apparent only near the front ; two or three short ribs exist 

 also in some specimens close to the margin on each of the lateral portions of the valves. 

 Beak incurved ; fissure triangular, margins of the valves deeply sinuated and biplicated in 

 front ; proportions variable ; two specimens measured — 



Length 7|, width Qh, depth 7 lines. 



7 Q f\ 



33 ' > >> U > 33 V ' 33 



Obs. This species does not appear to have attained the dimensions of the preceding 

 one, although some examples described by Professor Schnur from Priini in the Eifel have 

 exceeded by two or three lines the largest specimens hitherto observed in Great Britain ; 

 it is also easily distinguished from P. brevirostris by its general shape as well as by the 

 biplication of its front and lateral ribs. 



K 



