88 A. E. Verrill — Stitdy of the family Pectinidce. 



similar but smaller one, on each end or on the posterior only, above 

 the auricular ridge, forming " auricular crurre." 



In many of the younger shells one or both of the internal ribs may 

 be lacking, as in other species of Propeamiisium. 



The cardinal ridges are rather broad, flat, and crossed by numerous 

 very small transverse incisions and denticles. These are more 

 strongly developed than in many allied species, but less so than in 

 Cyclopecten nanus V. and B., and several other species examined. 

 Some examples of Chlamys irradians excel in this respect (see pi. 

 xvi, fig. 6). 



The resilial pit is peculiar, for in the upper or left valve it pro- 

 jects distinctly beyond the hinge-plate, as a spoon-shaped process, 

 but in the lower valve it is excavated in the sunken and oblique 

 median notch of the hinge margin. 



The byssal notch is broad and shallow, its margin not incurved, 

 and without any pectinidial teeth. The auricles are very unequal ; 

 the posterior one has a prominent angle. 



The upper valve is elegantly cancellated, and often mottled with 

 yellowish white on a reddish ground-color. The lower or right 

 valve is white and covered with strong, even concentric ridges or 

 laminae. The lower valve has a marginal flattened area which fits 

 closely against a similar, flattened, submarginal area of the upper 

 valve. 



Those in alcohol had the soft parts poorly preserved, but there 

 were about six rather distant, black ocelli visible through the trans- 

 lucent shell. 



Off the eastern coast of the United States in 43-317 fathoms, West 

 Indies in 84 to 450 fathoms, Blake Exped. 



This species is here referred to Propeamusiuni on account of the 

 two internal lirse or ribs within the body of the shell, for the pres- 

 ence of such lirae is the distinctive character of this genus. In other 

 respects it agrees about as well with Cyclopecten. These two groups 

 are very much alike in form, sculpture, and the unlikeness of the 

 two valves. The present species is, therefore, intermediate between 

 the typical forms of the two groups. 



Analytical Key to the genera of Pectinidce. 



The following table is not strictly a natural one, as to the sequence 

 of the genera, but is as nearly natural as could be made consistently 

 with convenience of use. 



