CREPIDULA. 



GENERIC CHARACTER 



Shell free, univalve, irregular, ovate or oblong, convex, 

 somewhat patelliform, with an epidermis ; spire very short 

 or obsolete, apex obvious, obliquely inclined, towards the 

 margin ; within horizontally divided about half the length 

 by a diaphragm ; muscular impression lunate. 



Jlnimal more or less depressed, oval, curved in the pos- 

 terior part ; mantle very thin, without marginal tentacula ; 

 foot not thick, small and rounded ; body each side of the 

 head auriculated ; head emarginatc before ; tentacula two, 

 subcylindric, or subconic, slightly contractile, with the eyes 

 near their exterior base ; mouth in the cmargination, with- 

 out teeth ; branchial cavity very large, situated obliquely 

 on the anterior part of the back, containing a fascicle of 

 long branchial filaments, which extend forward and at tip 

 float on the right side of the neck ; anus on the right side. 



OBSERVATIONS. 



These are marine shells attaching themselves to various 

 objects. At least many of the species have no locomotion, 

 passing their whole life in one spot, and being moulded 

 upon the surface of their resting place, exliibit its curva- 

 tures and inequalities. 



Lamarck separated the species from the Linnean Patel- 

 la, forming a very natural and very distinct group. For 

 although it exhibits a slight similarity to Septaria, Fcruss. 



