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 denned, with the line 

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

 of doubt. 



Calypte^ia,* Lam, 1801. 



Patella (spec.) Linn. 

 Galeiuts. Humph. 1797. 

 Calyptka. Id. 



Calyptrus. Montf. 1810. 

 Infundtbolum. J. Sow. 1815. 

 Trochita. Schum. 1817. 

 Mitrularia. 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, distin- 

 guished 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 larger 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 Calyptrsea in all essential points of structure, differing only 

 in the proportionate extent of the anterior part of the foot, and dorsal groove of 

 the mantle." Dispotea, 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 

 on 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. KaXvTTTfta, a covering. 



