CONCHIFERA. 



295 



Animal oblong, margins of mantle in all parts simple, 

 closed only to form a short, and more or less perfect tube 

 in the anal region; foot cylindrical, with a more or less 

 cylindrical byssal gland at its base ; branchise elongate ; 

 labial palpi triangular and pointed.* — Many species ; 

 also fossil. 



Attached by a byssus to the rocks of which they some- 

 times almost cover the surface ; the byssus is very strong, 

 and several of the species construct a sort of enveloping 

 nest from it. This has been observed by Mr. Forbes. 



Modiolaria. Beck. (Lanistes Sow.) — Shell rather oval, 

 with radiating furrows at both ends, otherwise not essen- 

 tially different from Modiola. Animal, with the mantle 

 cloven the greater part of its length, behind produced into 

 a short tube, before which the mantle edge stretches out 

 into the form of a round lobe ; the foot is worm-shaped, as 

 long as the shell, and forms a delicate white byssus. — 

 Several species ; also fossil. 



The greater number of the species live in the European 

 and Northern seas ; sometimes found in the mantle of the 

 Ascidia, or in a web, formed by the byssus. 



Crenella. Brown. (Myoparo Lea.) — Shell equivalve, 

 very inequilateral, tumid or compressed; 

 surface covered with an epidermis, and 

 either entirely or partially ornamented by 

 stride, radiating usually in two diverging 

 fasciculi from the beak ; hinge margin 

 toothless, generally crenulated ; ligament linear, internal ; 

 two unequal muscular scars, pallial impression obscure. 

 Animal, oblong, its mantle closed anteriorly, open in front 

 and in the branchial regions, where the margins though 



* Forbes's British Moll. 



