164 ARCIDiE. 



by a Pinna of the comparatively stout cords or cables 

 by which it is permanently anchored to the sea-bottom. 

 Most of the Conchifera appear to be byssiferous. 



A species of Limopsis closely allied to the present 

 has been taken by Mr. M f Andrew on the coast of Upper 

 Norway, in from 70 to 100 fathoms, and was referred 

 by him to the Pectunculus pygmaus of Philippi. Sars 

 found the same species also on the Norwegian coast, but 

 considered it to be the P. minutus of Philippi. Both 

 species are fossil. The L. pygmaea of Searles Wood 

 from our Coralline Crag is certainly different from Mr. 

 M f Andrew's shell. In Adams's ' Genera of Recent Mol- 

 lusca' the Norwegian species is called " L. borealis, 

 Woodward." The inside margin of the shells found by 

 M f Andrew and Sars is notched or crenulated, but in 

 L. aurita it is plain or entire, and the contour of this 

 last shell is rather less oblique. Whether the crenu- 

 lated margin is a specific character in Limopsis may be 

 open to doubt. Of two species of Astarte {A. sulcata 

 and A. triangularis) usually having notched edges, a 

 variety of each is not uncommon which has smooth 

 edges ; and specimens are occasionally found possessing 

 both characters, or having the inner margin partly 

 notched. 



Genus IV. PECTUN'CULUS % Lamarck. 



PL IV. f. 4. 



Body nearly circular, or suborbicular : mantle open in front, 

 as well as on the anterior side, and sometimes folded on the 

 posterior side into a very short excretal duct ; the other part 

 of the mantle on the posterior side has its margin furnished 

 with numerous ocelli or eye-like points : foot large and thick, 



* A small scallop (Pliny). 



