EARLY DEVONIC HISTORY OF NEW YORK AND EASTERN NOfcTH AMERICA 35 



well defined in early growth but becoming obscure in later stages. Ante- 

 rior extremity well rounded, the lower margin of the valves incurving 

 medially and rounding again to the broader and rather blunt posterior 

 extremity. The surface of the valves is rendered concave medially by a 

 broad not sharply defined sinus passing from the umbones to the lower 

 margins. Contour quite regularly convex on each side of the sinus. The 

 length of the shell is somewhat less than thrice the hight. Surface smooth. 

 The hinge structure of this shell has not been definitely determined but the 

 species is provisionally referred to Macrodus. 



Species name. Professor L. W. Bailey, Canadian geologist. 



Horizon. No. n. 



Janeia sp. ? 



The Dalhousie beds contain modiomorphoid shells of small size with- 

 out greatly expanded posterior extremity or well defined umbonal ridge ; 

 indeed they are notable for the absence of features which may guide to their 

 positive generic determination and I am disposed to place them with Janeia, 

 the Devonic species of which afford expressions of this kind. 



Horizon. N os. 9, 1 1 . 



(Pectunculus ??) plutonicus nov. 



Plate 6, figures n, 13 



Views are given on the plate referred to of a subspherical pelecypod 

 with an exterior singularly arcoid in expression, indeed suggesting the 

 genus to which in all probability it can not belong Pectunculus. Such 

 specimens as these figured retain the shell substance which is heavy and 

 thick, have highly gibbous umbones and overarching incurved beaks. The 

 ligament area extends for the entire length of the hinge, is very broad, the 

 two surfaces in conjoined valves sloping toward each other at a sharp angle, 

 and is deeply striated longitudinally. It is this ligament area taken in com- 

 bination with the contour of the shell that gives it the aspect of a Pectuncu- 

 lus. Every effort to separate the valves in order to express the true char- 

 . acter of the hinge has been unavailing but this will eventually become 

 known and a correct generic assignment of the species made. The surface 

 of the shell is marked only by concentric growth lines which do not inter- 

 rupt the general smoothness of the exterior. The characters of the shell 

 are sufficiently distinctive to justify the use of a species name even though 

 the generic structure is still undetermined. 



Together with this large and rotund species occur others of less con- 

 vexity and without any defined ligament area but with similar outline and 

 a very like relationship of the valves. Such shells are shown on plate 9, 

 figures 10 and 1 1. These may prove to be of the genus Edmondia but the 

 figures given serve only to indicate the presence of this species in the fauna. 



Horizon. No. 8. 



