50 



WEBB : BRITISH SPF.CIES OF TESTACELLA. 



External Characters. 



There are one or two points with regard to the external 

 characteristics of these slugs, that might be mentioned before 

 beginning to consider their comparative internal anatomy. 



The dorsal lines, or preferably dorsal furrows, were used to 

 some extent as a distinguishing feature in the table of external 

 characters, for the determination of the British species given by 

 the writer in this journal '■■ ; but, in tlie case of the two species, 

 scntulum and halioiidea, the size of the angle contained by the 

 furrows was merely mentioned as being the greater in the latter 

 species. 



Mr. Taylor f pointed out a more definite difference, in that 

 the furrows (lie calls them lateral however, the lateral grooves 

 in the writer's table being those which branch from the dorsal 

 ones, after the manner of the side veins from the mid-rib of a 

 leaf) meet outside the shell in 7". scntulum; and Mr. Lionel Adams, 

 in the second edition of his Manual | uses this feature as a 

 distinguishing one. The writer has found the distinction a 

 constant one, and the following descriptions are quoted from the 

 Manual : — 



Dorsal furrows 



when the anima! is 

 extended. 



Tcstacelta scutulum, Sow. 



Branching off from a 

 point outside, and just 

 in front of the shell." 



TcstaccUa lialiotidea, Drap. 



Branching out from 

 point just under the 

 shell." 



Since the table above referred to was published, the writer 

 has noted several variations from the more generally occuring 

 forms upon which it was based. 



Judging from the Conchological Society's list, and ]\Ir. 

 Adams' Manual which follows it, one would imagine that either 

 Tcsiacellae did not vary, or that no variations had been noted, 

 for instead of the long series of varietal names that is usually 

 presented to the reader under the heading of each species, there 

 occurs after the description of T. maugei alone, but a single 

 variety, viyidans (Morelet). To the writer the absence of these 



* Volume iv. (1895), p. 76. 



t Journal of Conchology, volume v. (July, 1888), p. 339. 



t The Collector's Manual of British Land and Fieshvvater Shells, and edition (1896), 

 pp. 40 and 41. 



