G8 PECTINID.E. 



which radiate from the beaks and are crossed by coarse flexuous 

 striae ; the edges of the ears on the lower valve project very 

 slightly ; byssal sinus deep : hinge-line straight, finely notched 

 or serrate at its edge: cartilage rather large: ligament ex- 

 tremely slight: hinge-plate very narrow, microscopically striate 

 across ; transverse rib slight, and not much raised on each 

 side of the cartilage-pit, which is proportionally more open 

 than in any of the foregoing species : inside slightly nacreous, 

 finely and closely striate lengthwise, or furrowed when the 

 outside is ribbed ; margin sometimes notched or crennlated : 

 muscular scars indistinct except in aged specimens. L. 0*575. 

 B. 0-55. 



Yar. suborbicularis. Shell larger, with the slope much 

 higher than usual, and considerably narrower behind: ears 

 smaller. L. 0-7. B. 0-7. 



Habitat: Shetland, Skye, Larne (co. Antrim), Birter- 

 buy Bay (co. Galway), Guernsey (J. G. J.) ; Exinouth 

 (Clark); in gravelly sand, 18-80 fathoms. It is a rare 

 species. The variety is remarkable. I obtained only a 

 single valve by dredging off the north coast of Shetland in 

 86 fathoms. Although of much smaller size, this variety 

 resembles in shape and other respects the P. Gerardii 

 of Nyst, one of our Coralline Crag fossils. The foreign 

 range of P. Testa extends from Norway to Algeria and 

 the iEgean. Asbjornsen gives the depth at which it is 

 found in Christiania fiord as 10-20 fathoms. 



This beautiful species differs from P. tigrinus, with 

 which it is sometimes found, in the following particu- 

 lars. The shell is broader, flatter, and thinner; the 

 ribs, when they occur, are scaly or prickly ; the punc- 

 tures are very strongly marked and arranged in squares; 

 the beaks are much less prominent and raised ; the ears 

 are not so unequal ; and the inside margin is seldom 

 crenulated. Forbes and Hanley considered it to be a 

 variety of P. striatus ; but Malm has satisfactorily 

 shown some of the points of difference between these 



