EARLY DEVONIC HISTORY OF NEW YORK AND EASTERN NORTH AMERICA 207 



but in tlie most ventricose specimens, the umbonal region is so exceedingly tumid, that 

 it projects a little over the hinge line; beak not distinct from the cardinal edge. Dorsal 

 valve witli a curvature corresponding to that of the ventral, leaving but a thin space for 

 the animal; area half the size of that of the opposite valve, and forming an obtuse angle 

 therewith. 



There are three or four spines on the cardinal edge of the ventral valve, rarely pre- 

 served. They incline outwards at an angle between 40° and 50 . I have seen no speci- 

 men with all the spines preserved, but it seems probable that those nearest the beak are 

 the shortest. 



Surface with fine, closely arranged, convex ribs, eight to ten, on an average in the 

 width of one line, increasing both by bifurcation and interstitial addition, and crossed by 

 exceedingly fine concentric striae, of which there are l)etween thirty and forty in one line. 

 The ribs are slightly flexuous and of a very uniform size. In some specimens, the ventral 

 valve exhibits an obscure mesial sinus extending from the beak to the front margin. 



To the excellent description and illustration of this species given by 

 its author we have little to add. The specimens which we refer thereto 

 show some variation in outline from the usual transverse shape, occasional 

 shells being more extended in front, with narrower and flatter cardinal slopes. 

 While the contour is generally gibbous longitudinally with quite abrupt 

 anterior and posterior slopes. The more elongate shells have these slopes 

 more gradual. The surface striae in many cases vary more than is indi- 

 cated by Billings and may increase suddenly and rapidly at a growth line 

 by the implantation of numerous finer lines. Frequently on the ventral 

 valve the median stria is larger than the rest, but relatively less so than in 

 C h. canadensis. The striae of the ventral valve at times becorne very 

 obscure in adult growth over the pallial and lateral regions and then the 

 surface shows the fine concentric lines otherwise scarcely visible. 



The interior of the ventral valve shows pretty widely ^xplanate fan- 

 shaped muscular scars separated by a short but stout septum. And on the 

 dorsal valve the reniform ridges are quite distinct. The cardinal features, 

 which Billings specially illustrated, and the denticulation of the hinge, are 

 clearly observable in some of our specimens though the denticles are but 

 short and ill developed. This crenulated hinge also occurs in species of 

 the Gaspe sandstone and is considered on a following page. 



. Dimensions. An average normal specimen measures 22 mm in width 

 on the hinge, 12 mm in length. Another with the same length of hinge has 

 a length of 14 mm. 



Localities: Mr Billings cited the species only from Little Gaspe in 

 limestone 8. We have it also from this locality and from Indian Cove, 2 

 miles east of Grande Greve. It seems to be peculiar to the upper t»eds of 

 the series. 



