^ LAMELLIBRANCHIATA. 



Jeff revs" of which a couple of very small pieces show similar characteristic, concentric folds which 

 mark the Peclcti of the Norwegian Sea, whilst others and larger pieces obviously belong to 

 another type. The specimen from the "Porcupine" Expedition is entire, but only ca. lo "'"'. long. — 

 Under the name of P./ragilis, further, there were found a right and a left valve from the waters of 

 Spitzbero-en, sent by H. Friele, but the left valve was in pieces; these valves proved to be comp- 

 letely identical with a specimen from the "Ingolf" Expedition, which I had sent Dr. Johansen for 

 comparison. 



The explanation of the matter is now quite clear; Jeffreys has identified the fragments from 

 the "Valorous" Expedition with the deep-water Pcctoi taken by the Norwegian North-Atlantic Ex- 

 pedition a year later; the diagnosis has been based on the specimen from the deep basin of the Nor- 

 wegian Sea, but as the left valve of this specimen was in pieces, Jeffre)'S has made use of the 

 larger fragments from the "Valorous" Expedition ; these belong, however, to quite a different type, 

 obviously without striation, since they reminded Dr. Johansen of P.groenlaiidicus — from this has 

 come the passage, which has caused so much trouble to authors: "the lower valve has .... no longit- 

 udinal striae". Later, in the paper of 1879, Jeffreys' artist has replaced the fragmentary left valve 

 in another way, namely, by placing the right valve on its convex side, taken its contour and furnish- 

 ing it with a sculpture, as if it was seen from the outer side. I need not refer to the manner in 

 which other authors have sought to explain the difficulties caused in this way. 



It is not at all certain, therefore, that the fragile Pecten of the Norwegian Sea with concentric 

 folds is identical with the North Atlantic P.fragilis Jeffreys from the "Valorou.s" E-xpedition; on the 

 contrary, I feel convinced, that there are two species, nearly related yet distinct, and for the following 

 reasons. 



From the Western Atlantic off the United States (37°38'4o" N. L., 73°i6'3o" W.L., 1423 fm.) 

 Verrill and Smith have described a Pcctoi it 11 da fits, which agrees in all regards with the Pcctcii 

 of the Norwegian Sea except that titc cars of the shell are considerably larger, for which reason it 

 must be considered a different species from the arctic deep-water form. It is more reasonable to 

 conclude, therefore, that the fragments of the Atlantic P.fragilis Jeffr. from the "Valorous" Expedition 

 and the small specimen from the "Porcupine" belong to the same species as P.iiiidattis Verrill & 

 Smith than to the species living in the deep water of the Norwegian Sea under quite different 

 physical conditions. P'or this reason I have given the form from the Norwegian North-Atlantic and 

 "Ingolf Expeditions a new \V3.\\\^: frigidiis. meaning, that it lives at temperatures which are constantly 

 under 0° C. 



In the same year (1885) in which P. niidatiis was founded, E. A. vS m i t h described a Pecten 

 pudicus from the Southern Ocean E. of Marion Island (46°46'S. L., 45^31' E.D., 1375 fm.), whicli likewise 

 shows a great resemblance to mv form from the northern cold area, but has in common with 

 P. undatus the relatively large ears and will perhaps on direct comjiarison prove to be identical with 

 the latter. 



Pecten (Hyalopecten) dilcctus Verrill &. Bush from the east coast of North America, 1813 fm., 

 will also probably prove to belong to P. inidatus as its younger developmental stage. 



