M. Reinhardt on Carterodon sulcidens, 417 



are proved to be facts, by some specimens of these shells com- 

 bining in one individual what have been regarded as two or more 

 species. If, in such cases, all the Crepidulce and Calyptrace from 

 one geographic district were arranged together, we should see 

 that the species of each of those districts exhibit similar varieties, 

 and that the species which have been made on the form of 

 the shell are in fact varieties, from similar causes, of different 

 species. 



Unfortunately the animals of these genera show themselves so 

 little beyond the shell when the animal is alive, and afford so 

 few characters as they come to us preserved in fluid, that we 

 can expect but little assistance from them in the determina- 

 tion of the species. They have no operculum to help us ; yet we 

 may hope that the examination of the tongues of the different 

 kinds may help in determining the distinctness of the geographic 

 species ; but as yet no attempt has been made, except by Dr. Loven 

 and Mr. Thomson, to use the teeth for this purpose. It would be 

 an admirable subject for a young malacologist who can use the 

 camera lucida on the microscope to take up, as by so doing he 

 would be rendering most important assistance to the study of 

 Mollusca. *- 



XL. — Description of Carterodon sulcidens, Lund, By John 

 Reinhahdt*. Translated from the Danish by Dr. Wallich, 

 F.R.S., Vice-Pres. L.S. 



Lagoa Santa, 1 9th July 1 85 1 . 



Among the heaps of small bones, so frequently met with in 

 the limestone caves of this part of the Brazils, and which owe 

 their existence to Strix perlata, Licht., are often found skulls, 

 more or less broken, of a small animal, belonging to the family 

 of Pig-rats, but distinct from the cognate forms, in having on 

 each side of the upper incisors, along the middle, a projecting 

 ridge, with a lateral, rather deep furrow. Dr. Lund founded on 

 these crania his Echinomys sulcidens, in his first treatise on the 

 extinct animal creation in Brazil f, which he subsequently 

 thought could be referred to the genus NelomysX, on account of 

 certain peculiarities in the dental system, and at last to Aula- 



* From a letter to Prof. L. Steenstrup ; communicated to the Associa- 

 tion of Natural History at Copenhagen, at the meeting on the I4th Nov. 

 1851. 



t Blik paa Brasilicns Dyrevcrden, &c. (View of the Animal World of 

 Brazil before the last Revolution of the Globe.) First memoir. Introduce 

 tion, p. 23. 



X hoc. cit. Third mem. p. 30. 

 Ann. ^ Mag. N. Hist. Ser. 2. Fb/.x. 27 



