I.AMI'I.I.HIRANCIIIATA 



33 



size, only in a few does the margin of the left valve extend a trifle beyond that of the right, without 

 however bending over it" and p. 453 (under Pecten Hoskynsi Forbes var. ?najor Leche): "in all very 

 thin-shelled Pecten-forms the weakest valve gives way at the edge, when the animal retracts strongly 

 on dying, thus producing the characteristic concavity, which runs concentrically with the margin of the 

 shell, the sculpture markings on the right valve giving this a greater firmness". 



In his diary written on the Danish East Greenland Expedition of 1900, the young zoologist 

 Soreu Jensen, since dead, entered the following observations regarding P. groenlandicus : ". . . . this 

 small bivalve is able to swim when fully-developed. It opens and shuts the valves, beating the 

 water out during the latter process with considerable force and thus moving backwards through 

 the water. The specimens which lay on the bottom of a glass with water, could in this way "gape" 

 their way right up to the surface". 



Pecten frigidus Jensen. 

 PI. I, figs. 7 a— f. 



1876. Pecten fragilis Jeffreys, Ann. Mag. Nat. Hist. (4) XVIII, p. 424 (partim). 



1877. P./ragilis Friele, Nyt Mag. f. Naturvidensk., 23 Bd., 1877, II, p. 2. 



1879. P./ragilis Jeffreys, Proc. Zool. Soc. Loud., p. 561 (partim), PI. 45, fig. 1 ad dextram.'i 

 1879. P./ragilis Friele, Catal. d. auf d. norw. Nordmeerexped. bei Spitzbergen gef. Mollusken ; Jahrb. 

 Deutsch. Mai. Gesellsch. VI, p. 264. 



1901. P./ragilis Friele & Grieg, The Norwegian North Atlantic Hxped., Zool., Mollusca III, 



1 901. p. 8. 



1902. P. biscayensis Friele (non Locard), Moll. d. ersten Nordmeerfahrt d. Fischereid. "Michael Sars" 



1900; Bergens Museums Aarbog 1902, No. 3, pp.3, 15 & 17. 

 1904. P./rigidus Jensen, Vidensk. Medd. fra den naturhist. Foren. i Kbhvn. 1904. ^.305 (cum fig.). 



1904. P./ragilis Hiigg, Arkiv for Zoologi, Bd. 2, 1904, No. 2, p. 30. 



1905. P./rigidus Bavay, Mem. de la Soc. Zool. de France, T. XVII, 1905, p. 189, PI. 17, fig. 4. 



The shell a little higher than lone, irregularly stiborbicular, with the anterior and lower 

 margins forming together a semicircle and the posterior margin sligthly arched or almost straight, 

 compressed, the right valve flatter than the left, translucent silvery white. The valves very thin, 

 fragile, with concentric folds, to the number of about 12 in the adult, broad in the middle of the 

 shell, narrowing towards the lateral margins, with numerous fine, elevated, radiating strife. The 

 auricles small, unequal, the posterior the smallest, faintly marked off from the shell, the anterior 

 distinctly marked off from the shell, the left triangular, the right with an acutely angulated sinus for 

 the byssus. Hinge-margin straight, pit for the cartilage very small, triangular; the internal surface 

 shining. Length 27"""., height 29 mm ., breadth 6.5 mm . 



Distribution: The ice-cold depths of the Norwegian Sea, from Spitzbergen down towards 

 Iceland, the Faeroes and Shetland, 579 — 1539 fm. 



9 The figure to the left represents, so far as the contour is concerned, the same valve the inside, but 



provided with a form and sculpture as if seen from the outside. 



The Ingolf-Expedition [I. $. 5 



