158 MOLLUSCA FROM THE CRAG. 



This genus is largely developed in the Crag formations, but appears to have 

 been subject to great variation. My' specimens are here separated and considered 

 as determinable into four species, which are, however, so ill defined, with the line 

 of specific demarcation so obscure, that their correct appropriation is still a matter of 

 doubt. 



Calyptr^a,* Lam. 1801. 

 Patella (spec.) Linn. 

 Galerus. Humph. 179". 

 Calyptra. Id. 



Calyptrus. Montf. 1610. 

 Infundibulum. J. Sow. 1815. 

 Trochita. Schitm. 1817. 



MiTRCLARIA. Id. 



Mitella. Leach, 1818. 



Gen. Char. Shell conical, clypeiform, depressed, subspiral, with the vertex nearly 

 central ; base more or less regularly orbicular, entire, and sharp edged ; interior cavity 

 furnished with a lateral appendage or septum, variable in form, externally smooth, 

 rugose, costated, or sometimes covered with imbricated spines. 



This genus has been separated by M. Lesson into several subgenera, distinguished 

 by the form of the internal diaphragm or appendage, which is exceedingly variable 

 both in shape and magnitude. Mr. Broderip has figured and described in the Trans, 

 of the Zool. Soc. 1835, a large number of recent species, belonging to the five Sections 

 into which they have been divided by M. Lesson, viz., Calyptraea, Calypeopsis, 

 Syphopatella, Crepipatella, and Crepidula, and says the differences are not such as will 

 entitle them to generic distinction, and quotes Mr. Owen's opinion in regard to the 

 animal, who says : " The soft parts of the animal of Crepidula are the same with those 

 of Calyptraea in all essential points of structure, diff'ering only in the proportionate 

 extent of the anterior part of the foot, and dorsal groove of the mantle." Bispotea, 

 Conrad, was intended for those species that have been called cup-and-saucer limpets, 

 in which the internal appendage resembles the subconical form of the external shell. 



The known recent species are marine animals, and most of them have been found 

 cm rocky coasts in warm climates. M. d'Orbigny describes one species from the 

 Cretaceous formation, which is, I believe, the earliest appearance of this genus. 



* Etym. KaXiiTrrpa, a covering. 



