EARLY DEVONIC HISTORY OF NEW YORK AND EASTERN NORTH AMERICA 33 



deep sockets beneath the beak of the left valve, the posterior one often 

 elongated and running subparallel to the hinge margin ; the inner sides of 

 these dental ridges, when well preserved, are seen to be finely striated trans- 

 versely, suggesting the appearance of Nucula, though these transverse lines 

 do not develop into distinct pits as in that genus. 



The right valve has processes corresponding to these pits. The shells 

 have regularly closing margins all around and are more or less transverse 

 with slightly projecting umbones. Their hinge structure indicates affinity 

 with the Cardiniiclae. Of these shells two species were described, C. 

 gregarium and C. sociale, both from the Siegen greywacke of 

 Singhofen and neighboring localities where they seem to be extremely 

 abundant and of gregarious habit. 



It is interesting to note that the most abundant of the pelecypods at 

 Dalhousie is of this type. 



Carydium gregarium Beushausen 



Plate 5, figures 6-12 

 St-t- p. 141 



Carydium gregarium Beushausen. Lamellibranchiaten der rheinischen Devon. 

 1895. p. 156, pi. 14, fig. 1-6 



Between these very abundant shells at Dalhousie and those described 

 by Beushausen I can find no distinction. These are small, slightly inequi- 

 lateral shells with considerable convexity ; beaks not far in front of the 

 middle with full umbones ; crescence line full and rounded but not promi- 

 nent, and outline transversely oval, expanding posteriorly. The surface of 

 these shells is smooth and they appear to have been without the fine con- 

 centric lines of Nucula and the Palaeoneilos which they resemble in the 

 features usually exposed. The hinge, so far as seen, is in accord with the 

 characterization of it as given by Beushausen and the adductor scars are 

 frequently apparent, the anterior being generally the more conspicuous. 

 The valves measure from 10 to 12 mm in length with a greatest hieht of 

 5 to 6 mm. 



Horizon. Nos. 9, 10, 11. 



Carydium elongatum Clarke 



Plate 5, figures 13-17 



Carydium elongatum Clarke. N. Y. State Mus. Bui. 107. 1907. p. 227 



This is distinguished from its associate C. gregarium Beushausen 

 by its longer and narrow valves which are quite regularly convex from a 

 transverse median line, the surface sloping thence uniformly above and 

 below, leaving the umbones depressed. The anterior end is visibly nar- 

 rower than the posterior though the latter is not greatly expanded. The 



