TESTACELLA. 141 



Shell solid : spire consisting of half a whorl : columellar fold 

 internal, very broad. 



This peculiar genus appears to form a natural family 

 of itself, when viewed with respect to the British Mol- 

 lusca only ; but it is connected with the Slugs on the 

 one hand through the genus Pa7i7iacella, which has no 

 representative in this country, and on the other hand 

 with the Snails through the Vitrina semilimax of Fe- 

 russac (also a Continental mollusk), which Oken called a 

 Testacella. The Testacella partake in some degree of 

 the nature both of a Slug and a Snail, having a long 

 naked body and a small shell placed near its tail. The 

 shell serves to protect the heart, liver, and other vital 

 organs. The Snail-slug was first made known by the 

 celebrated Reaumur in 1740 through the Academy of 

 Sciences at Paris, in consequence of a communication 

 made to him by M. Dugue from Dieppe, and which con- 

 tains an excellent account of the shape, habits, and mode 

 of reproduction of this curious mollusk. From that 

 period down to 1800, many observations were made and 

 recorded in France on the same subject ; but it was only 

 in the last-mentioned year that Cuvier, being struck by 

 the remarkable aspect of the shell, constituted for it, in 

 his ' Lessons on Comparative Anatomy,' the genus Tes- 

 tacella. This name was adopted both by Lamarck and 

 Draparnaud in 1801 ; but in the following year it was 

 erroneously altered by Faure-Biguet to Testacellus. This 

 slight history of the name is given to prevent a con- 

 tinuance of this mistake, which was adopted by Fe- 

 russac_, Sowerby, Gray, and other naturalists. By far 

 the most complete and valuable account, considered in a 

 conchological as well as a palseontological point of \dew, 

 which has been given of this genus, is contained in a 



