5/4 DR. GWYN JEFFREYS ON TUB MOLLL'SCA OF THE [June 17» 



Silicula fragilis 1 , Jeffreys. (Plate XLV. figs. 6, 6 a.) 



Body clear white ; foot axe-shaped. 



Shell ensiform or obliquely oblong, inequilateral, compressed, 

 thin, glossy, nacreous, and semitransparent : sculpture extremely 

 fine and numerous but irregular concentric striae, which are only 

 observable with a magnifying glass ; there are also occasional lines 

 of growth : colour white, under a pale brownish-yellow epidermis : 

 margins nearly straight at the back on the anterior side, rounded at 

 the other side, extended aud wedge-shaped at the anterior side, the 

 extremity of which is truncated, with a slight notch or indentation 

 in the middle, gradually curved in front : beaks placed near the 

 smaller end, at about one third the length of the back ; they are 

 small, rather prominent, and calyciform : lunule well defined, lance- 

 head-shaped, and elongated : ligament none : cartilage and pit 

 oblique : hinge-line long, nearly straight on the anterior side, and 

 gently curved on the other side : hinge-plate rather narrow : teeth 

 elongated, four on each side, somewhat like the lateral teeth in Tel- 

 Una, but overlapping one another, and not continuous : they are of 

 different lengths, those at each end being the shortest and strongest : 

 inside polished and iridescent, microscopically fretted towards the 

 front margin : scars inconspicuous. L. 0" 15, B. 0'3. 



'Porcupine' Exp. 1869: St. 16, 28. 



A. More or less angulated or pointed at the longer end. 



1. Leda pernula, Miiller. 



Area pernula, Mull, in Beschiift. Berl. Ges. naturf. Fr. iv. p. 57 

 (1779). 



L. pernula, B. C. ii. p. 158 ; v. p. 173 : G. O. Sars, Moll. reg. 

 arct. Norv. t. v. f. 1 a-d. 



' Porcupine' Exp. 1869 : St. 4, Loch Torridon. 1870 : Atl. 1, 2, 6, 

 9. One perfect specimen (but dead) and several valves of different 

 sizes, all being more or less smooth or destitute of concentric striae. 



Distribution. Arctic Ocean in the N. Atlantic southwards to the 

 Cattegat on the east aud Maine on the west, Novaya Zemblia, 

 Behring Strait ; 5-210 fms. 



Fossil. Post-tertiary or " glacial." N. lat. 82°, N.E. America, 

 Archangel, Scandinavia, Great Britain and Ireland ; 0-1360 ft. 



Being variable in shape and sculpture, this species has many 

 synonyms. 



^ 2. Leda mintjta, Miiller. 



Area minuta, Mull. Zool. Dan. Prodr. p. 247. 



L. minuta, B. C. ii. p. 155, pi. iv. f. 2; v. p. 173, pi. xxix. f. 6. 



'Porcupine' Exp. 1869 : St. 1, 23a, 25, North Channel, the 

 Minch, Little Minch, near Belfast. 1870 : Atl. 2, 9 (valves only, and 

 perhaps semifossil). 



Distribution. Arctic seas in both hemispheres, to the Cattegat 



1 Brittle. 



