66 A. E. Verrill — Study of the family Pectinidm. 



They are closely allied to P. striatum (pi. xviii, figs. 14, 14a) in form 

 and sculpture and, like the latter, might well be referred to Gamp- 

 tonectes. 



The second type-species (P. vitreum) is rather more distinct, on 

 account of the very slight differentiation of the posterior auricle, 

 which is small and resembles the condition seen in the very young 

 examples of other species. This feature is also j^resent in the other 

 species in a somewhat less degree, 



P. vitreum (pi. xviii, figs. 6-13) has a broad, round, thin hyaline 

 shell, with the auricles unequal ; the posterior auricle is short and 

 only slightly differentiated from the shell ; it has an obtuse dorsal 

 angle from which the margin slopes to the body of the shell, without 

 a notch or angle. It has a number of sharp, free, pectinidial teeth 

 and a long series of discarded ones above the byssal fasciole. Auric- 

 ular crurse are rather jsrominent. The byssal notch is deep, and the 

 byssus is well developed. It is used to attach the shell to branches 

 of gorgonian corals [Acanella, Primnoa), etc. The " camptonectes- 

 sculpture " is strongly marked. The mantle has rather few tentacles 

 and pigmented ocelli. 



This arctic and northern European species has been recorded ( Voy. 

 Challenger) from the E. Indies, 100-700 fath., and from off Japan, 

 345 fath., and off Patagonia (140 to 400 fath.) It is common on the 

 deep-water fishing grounds off Nova Scotia and Newfoundland, in 57 

 to 400 fathoms, and extends southward in deep water down to 1537 

 fath., off Chesapeake Bay. 



P. Tested is less hyaline, and the auricles are more nearly equal. It 

 has well-marked camptonectes-sculpture and radial riblets on both 

 valves. There are several pectinidial teeth. According to Jeffreys 

 (Brit. Conch., v, \y. 167), the animal of this species has two unequal 

 rows of slender tentacles, the inner row much the smaller. Ocelli 

 few, in two rows, those in the outer row unequal in size and position ; 

 those of the inner row are much smaller and more numerous. Foot 

 cylindrical. It swims actively and often attaches itself by a byssus. 



It has been brought up attached to a telegraph cable from the 

 depth of 1000 fathoms in the Mediterranean. 



My conclusion is that these two species must be placed in the same 

 section with P. striatum and P. tigrinum. Nor can I see any valid 

 reason why the four should not be placed in Catnptonectes. 



It is true that the " camptonectes sculpture " is found also in larger 

 species of allied groups when young (e. g. P. Clintoniiis)^ and also in 

 certain ribbed species of Chlamys, but in the typical forms referred 

 to Camptonectes it is the predominant sculpture through life. 



