104 BRITISH MOLLUSKS. 



There is no part of the British Isles in which this Clausilia may 

 not be found. It is the smallest of our four species, and the shell 

 is the most slenderly convoluted and darkest in colour, a rich cho- 

 colate-brown, with traces of the whitish hair hues noticed in 

 C. biplicata less disposed in patches. The animal of C. perversa is 

 of a dark mottled-grey colour, small and attenuated. 



Agreeably with the suggestion of Deshayes (Arn'm. sans Vert. 

 vol. viii. p. 201, note), I restore to this species the name given to it 

 by Muller, and very generally adopted by the earUer British 

 authors. It is true that Linnaeus had a Helix perversa, but it is a 

 large Malayan Biclimus (B. citrinus, Bruguiere), not a Clausilia. 

 Chemnitz's H. perversa is a Tahiti Partula, and Ferussac's H. per- 

 versa is the British Balea. Draparnaud separated Midler's Clau- 

 silia perversa, into two species, giving to them the names C. rugosa 

 and dubia, and Moquin-Tandon has followed Draparnaud, substi- 

 tuting the name nigricans for dubia, assuming, on the authority 

 apparently of Dr. Gray, that it was so named by Pulteney in 1799. 

 This is a mistake. There is no Clausilia nigricans in Dr. Pulte- 

 ney 's original work. The species under consideration is there cor- 

 rectly named C. perversa ; and in the edition of 1813, C. perversa 

 is incorrectly illustrated. The true C. perversa is there figured 

 with the name C. nigricans improperly given to it by Maton and 

 Backett. 



Balea perversa. {Enlarged.) 



Genus X. BALEA, Prideaux. 



Animal ; lanceolate, rounded in front, attenuated behind, blackish, 

 passing into grey, minutely speckled with dark tubercles, carry- 

 ing a slight sinistrally convoluted turreted shell, tentacles short, 

 upper pair approximating. 



