372 LITTORINID &. 
I conclude this still imperfect monograph by calling on the 
naturalists of this branch of science to make it more complete, 
by searching in their respective localities after the animals 
which continue to elude our view. 
The following Rissoe have not occurred to us alive :— 
R. striatuita, Montagu. 
R. striatula, Brit. Moll. iii. p. 73, pl. 79. f. 7,8. 
R. tactea, Michaud. 
R. lactea, Brit. Moll. i. p. 76, pl. 79. f. 3, 4. 
R. Zettanpica, Montagu. 
R. Zetlandica, Brit. Moll. iii. p. 78, pl. 80. f. 1, 2. 
R. crenutata, Michaud. 
R. crenulata, Brit. Moll. iii. p. 80, pl. 79. f. 1, 2. 
R. catatuus, Forbes and Hanley. 
R. calathus, Brit. Moll. iii. p. 82, pl. 78. f. 3. 
R. asyssicoua, Forbes. 
R. abyssicola, Brit. Moll. iii. p. 86, pl. 78. f.1,2; (animal) pl. J.J. f.3. 
R. crnertius, Montagu. 
R. cingillus, Brit. Moll. iii. p.122, pl.79. f. 9, 10; (animal) pl. J.J. f.4. 
R. anatina, Draparnaud. 
R. anatina, Brit. Moll. iu. p. 134, pl. 87. f. 3, 4. 
R. ventrosa, Montagu. 
R. ventrosa, Brit. Moll. iii. p. 138, pl. 87. f. 1, 5, 6, 7. 
I introduce three new members to this family, the Skenea 
planorbis of the ‘ British Mollusca,’ and the well-known Ceri- 
thium reticulatum of all authors. The ‘planorbis,’ which I 
have for the second time examined, appears to be absolutely 
a discoid Rissoa, allowing the necessary margin for specialties 
of the shape of the foot, operculigerous lobe, tentacula and 
opercula. These organs greatly vary in the Rissoe, and 
often differ more with each other, and the type, than even 
the discoidal ‘planorbis. Ought there not to be two 
sections in Rissoa,—one for the elongated Cerithium reticu- 
latum, which repeated examinations tell me does not exhibit 
a difference from it in any material point, and might, as 
respects the animal, be the type, instead of R. parva,—and 
