i8 



LAMELLIBRANCHIATA. 



As no living specimens were forthcoming, it may probably be taken as fairly certain, that 

 Pecten islandicns no longer lives at the islands. 



Remarks. The radiating ribs of the shell begin to appear in the young immediately below 

 the prodissoconch. In the beginning the shell is provided with very dense, concentric lines (PI. I, 

 fio-s. 4 c and d), which in the spaces between the longitudinal ribs give way later to a very characteristic 

 rasp-like structure (distinct under the lens) (PI. I, fig. 4 a). The longitudinal ribs themselves are often 

 smooth, but not rarely rough from down-turned spines or scales. The rasp-like sculpture is almost 

 always present, if the shell is not too much rubbed; it may be difficult to see or has disappeared only 

 in the cases, when the radiating ribs lie very closely and are covered with scales, but even on such 

 specimens it can as a rule be observed on the older parts of the shell (PL I, fig. 4b). Curiously enough 

 authors do not seem to have attached any weight to this good distinguishing character, and 

 Verrill has even recently established a special variety iiisciilpfa (1. c, p. 73, fig. 5) for specimens 

 with such structure; in my experience this is practically never wanting, when carefully sought for 

 under a lens. 



Some few of the Greenland and Iceland specimens belong to the variety, which Chemnitz 

 has described and figured in Conchyl. Cabinet VII, 1784, p. 318, Tab. 65, fig. 616: the shell is thrown 

 into undulating, radial folds. I have also a similar variety from Jan Mayen. 



Distribution. Pcctcii islandicits is an arctic species, but whether it is circurapolar, as is generally 

 stated, seems to me more than doubtful. It has been taken, it is true, at Labrador, West Greenland, 

 Iceland and Spitzbergen, in the Barents Sea and at the entrance to the Kara Sea, but it has not 

 been found in the Kara Sea nor in the Polar Sea of Siberia'); then it appears again in the Bering 

 Sea, but it has not been met with in the Polar Sea north of arctic America 2), any more than at the 

 high-arctic East Greenland. In the Atlantic to the south it reaches to Cape Cod and West Norway 3), 

 in the Pacific to Korea and North Japan 4). — Its vertical distribution extends in general from 5 to 

 50 fathoms, but sometimes it goes deeper down. 



Shells ancient in appearance have been taken at many places, where it is certain the species 

 no longer lives, e. g. at Bohuslan (Malm), in the Kattegat (C. G. Job. Petersen), in the North Sea 

 (Metzgeri, at the British coasts (Forbes &: Hanley) and off the west coast of Ireland ("Porcupine"). 



I) The Dijmphna-Exped., whicli made many dredgings in the Kara Sea, only got a single small specimen, and it 

 was not taken in the Kara Sea itself, but in the entrance (Jugor Strait). Nor was it found by the Vega-Exped. in the Polar 

 Sea of Siberia. 



-) Under the distribution of P. islainiiciis, Posselt (1. c, p. 15) notes "Wellington Channel" and Belcher as his authority. 

 But on looking up Belcher: "The last of the Arctic voyages" (1S55), where P. islandicus is certainly noted among the 

 Molluscs collected by the Expedition and determined by Lovell Reeve (Vol. II, p. 396), we find the locality given as 

 "Lievely, Greenland'', i. e. Godhavn on Disko Isl. in W. Greenland, which was touched at by the Expedition both on the 

 outward and homeward voyage. "Lievely" is the name given by the English whalers to Godhavn. 



3) The southern boundary lies right down about 59°N.L., where Dr. O. Nordgaard in 1902 took a specimen off 

 the mouth of Lysefjord (Bergens Museums Aarbog 1903, No. 8, p. 36); Dr. Nordgaard kindly permitted me to see this 

 specimen, which was 45 mm. high and taken at a depth of ca. 24 fm. At Bergen already, where M. Sars found it, though 

 only as small, dwarf-like specimens (50mm. high), P. is/aiidicus is rare, as it is not mentioned in Friele's or Norman's lists of 

 the MoUuscan fauna of Bergen Fjord. I have had the opportunity of seeing two specimens from the immediate neighbourhood 

 of Bergen, taken by Dr. Nord gaard, the one in Radosund at a depth of ca. 5ofm. (height of specimen 29.5 mm.), the 

 other, of the same size, in Alvaerstrommen at a depth of i6 fm. along with Pecten opercularis. 



4) From Engineer Schonau of the Great Northern Telegraph Co., our Museum has received a specimen from tlie 

 coast of Korea and one from the waters S. of Wladiwostock (42°I5'N. L., 130=43' E.L..). 



