CREPIDULA. 



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TESTA transversim elliptica, ovata, vel oblonga, 

 dorso plerumque convexo, subtus cava; spird 

 aut nulla aut brevissima, vertice ad marginem 

 suboblique inclinata. Labium internum com- 

 planatum, acutum, edentulum, latum, lami- 

 nam horizontalem, aperturam partim claudente, 

 efformans; externum acutiusculum, integrum, 

 Impressiones musculares intern ae. 



A Genus separated by Lamarck from the Linnean Patella, 

 and named Crepidula from its resemblance to a slipper. 

 Lamarck thinks tliat perhaps among- the testaceous Gas- 

 teropodesy no Geuus is so eminently distinct as the Crepi- 

 dula^ not only in respect to the animal, but also to the 

 shell. We regret that we are compelled to differ in opi- 

 nion from so celebrated a conchologist and to state as 

 our conviction^ that it is very nearly related to Calyp- 

 trcea, so that it justly assumes the place assigned to it by 

 Lamarck and must follow CalyptrcBa closely, but it cannot 

 be considered as connected with Trochus. We have al- 

 ready, in describing the last named Genus, pointed out 

 the marks of discrimination between the two genera : 

 and in treating of Navicella we have shown wherein that 

 differs from the present Genus, so that we may now pro- 

 ceed to describe Crepidula; the following are its charac- 

 ters : shell transversely elliptical, oblong or ovate, very 

 rarely almost orbicular, the outside being almost always 

 convex, though sometimes concave^ but as the animal 

 remains generally stationary for a considerable period, 

 the form of the shell is naturally modified by that of the 

 rock or other substance to which it adhei'es, so that it 

 may properly be considered as an irregular shell. The 

 spire, if indeed it can be called a spire, whenever there is 



