424 Dr. .r. Gwyn JeftVcys on 



XLII. — New and peculiar Mollami of the Pecten, Mytilua, 

 and Area Families jyrocured in the ' Valorem ' Expedition. 

 By J. GwYN Jeffreys, LL.D., F.R.S. 



Pectinidae. 



Pecten fragilis*^ Jeffr. 



Shell roundish, equilateral, much compressed or flattened, 

 excessively thin and brittle, of a paper-like consistency, semi- 

 transparent, rather glossy, and somewhat iridescent : sculpture^ 

 in the upper valve 15-20 concentric ribs or undulating folds, 

 which do not extend to the sides, besides numerous longi- 

 tudinal fine and raised strias, which latter radiate from the 

 beak and cover the whole surface ; the sides are otherwise 

 marked by close-set lines of growth only ; the lower valve 

 has a few slight concentric ribs, but no longitudinal striae : 

 colour silvery-white : margins semicircular in front, and 

 sloping gradually towards the hinge-line, below which on each 

 side tliere is a gentle curve or depression : heahs very small 

 and rather prominent : ears small but broad, equal in size, 

 right-angled : hinge-line straight : cartilage-jiit very small, 

 triangular : hinge-plate broad and smooth : inside pearly : 

 muscular scars i\\co\\s,\nc\\o\xs,. L. 0'35. B. 0"35. 



'Valorous' Expedition: Station 9, 1750 fathoms ; St. 12, 

 1450 fathoms ; St. 16, 1785 fathoms. Norwegian Expedi- 

 tion, 1876, 1000-1500 fms. Fragments only. 



This s])ecies belongs to the section or subgenus Pseudamus- 

 sium of Klein, along with Pecten groenlandicus, P. vitreus, and 

 P. similis. 



A specimen from 1450 fathoms is permeated by the same 

 curious branching sponge (?) or organism that infests so many 

 shells from deep water and has been considered a Fungus by 

 some naturalists. 



Genus AMUSSlUMf, {Amusium) Rumphius. 



Shell inequivalve, more or less circular, flattened, smooth 

 or variously sculptured, furnished inside with slight ribs, which 

 radiate from the hinge and are not impressions of outside 

 markings, but are quite irrespective of them. 



The institution of this genus has been attributed by every 

 author to Klein ; but Rumphius (the " Plinius Indicus ") has 

 precedence of him by nearly half a century. The type of 



• Brittle. 



t Something exactly and evenly planed. 



