70 COXTRIBUTIONS FOK SYSTEMATIC CATALOGUE AQUATIC SHELLS. 



Pahtdestnna LegramUana and Wisema)iia7ia. Brazier. Pro. 

 Zool. Soc. London, p. 678, 1871. 



Amnicola Pefferdiana. Brazier. Pro Linn. Soc. N.S. 

 Wales. Vol. 1., p 19, 1875. (Tenlson-Woods.) 



Bytliinella exigua. Tenison -Woods. Pro. Royal Soc. 

 Tas., 1878. 



Animal, witli a narrow foot which is expanded in front,, 

 opaque, white shaded with very pale bluish-grey. Tentacles, 

 lon^', slender and pointed. Eyes plainly visible, under the 

 lens, at the outer base. liosfrnin, thick, projecting and 

 wrinkled. The tentacles and rostrum shaded with dark 

 bluish-grey. 



Op'-rculum, thin, yellow-horn, paucispiral. 



Dentition. The central basal lobe of the median tooth is 

 mucli produced, the first lateral is very much bent, and has 

 from 12 to 13 small rounded denticles thereon. In the second 

 they are also of the same rounded form but are not con- 

 tinuous. 



Formula of denticles, ^ — ^ ; 12 to 13 ; 11. 

 o — o 



Var. A. Legrandiana. Brazirr. 



Shell, conical, with the last whorl keeled below the suture, 

 and furnished with small, solid, stunted, hair-like spines. 

 Aperture ovate. 



Hahifaf — Widely distributed. Streams and jiools near 

 Hobart and Launcestou. Huon River, Elizabeth River, 

 River Mersey . 



Var. B. UNiCARiNATA. Teiuson-Woods. 



Shell, conical, thin, last two whorls with one interrupted 

 keel. A2)eriure, ovate. 



Habitat— With the last. 



Var. C. 



Shell, elongately conical, tapering, narrow. 



Aperture, narrowly ovate. 



Habitat — On stones and mud within the influence of salt 

 water. River Tamar and other [)laces. 



The " minute shining ovate scales" referred to l)y the Rev. 

 Mr. Woods are simply an incrustation of the frustules of 

 Cocconeis, a species of Diaioviaceiv. This specie is extremely 

 variable in form, size and ornamentation ; for these reasons I 

 have taken the ]»lain, unadorned minute blackish shells, so 

 abundant in our streams, as the type of the specie under which, 

 with the three extrememodifications given, the great majority 

 of the examples generally to be obtained may be arranged. 



In size, with the relative length of spire and aperture, it 

 varies almost indefinitely, so much so that almost every little 

 stream or pool has its own special variety, so that it is quite 



