Botany and Zoology. 271 
togyrus, &c. Even those who have admitted these new genera, however, 
still differed in regard to their family affinities, some placing certain of 
them in the Melaniide, others in the Rissoide, Viviparide, Littorinide, 
&e., while still other conchologists proposed to establish for their recep- 
tion a new family, Amnicolide. 
After a thorough and searching pba aan of the whole subject, 
eeecsarly of the structure of the softer parts and the dentition of 
any. of these types, Dr. Stimpson arrives at the conclusion that th 
litle snails all belong to zy Rissoide, to which they had in part been 
relerred by H. & A. Adams; though he also includes in the family the 
genera Lithoglyphus and Pateilencinn, (referred by those authors to the 
Littorinide), as well as several new genera he finds it necessary to estab- 
lish. He likewise suggests that Pyrgula, Tricula, Cecina, and Blan- 
fordidia probably belong to this group; while he excludes from it the 
genus Barleea, which had been included by H. & A. Adams. 
fter thus eliminating the extraneous genera, and including others 
ROG previously known to belong to this family, he gives a full and clear 
dia lagnosis of the group, by which it can rez idily be distinguished from 
the families Littorinide, Viviparide, Truncatellide, Melaniide and 
evade: with which it is more or less nearly allied, or has in part 
been confounded. He then defines the aphapeda six sub-families, into 
which the pi is found to be naturally divisible: 
ry Py ihiniine, including Bythinia Gray. 
Rissoinine, including Ressoina D’Orb. 
: Rissoine, including Rissoa Frem., Cingula Flem., beer Risso, and 
Onobia, Setia, Ceratia and Fenella H. & A. Adam 
4, Skeneine, including Skenea Flem. 
5. Hydrobiine, including Hydrobia Hartm., Littorinella Braun., Amni- 
rt : 
Tricula Benson, Pyrgula Christ. & Jan, Paludestrina D’Orb., 
Tryonia Stm., Potamopyrgus Stm., Lithoglyphus Muhlfeldt, Flumi- 
nicola Stim. Gillia Stim., Somatogyras Gill, and Cochliopa Stim. 
6. Pematiopin, including Pomatiopsis, Tryon. 
@ memoir is mainly devoted to the subfamilies Hydrobune ae 
Pomatiopsine. Of the genera belonging to the former, extended de- 
scriptions, and excellent outline cuts illustrating the shell, animal, deth 
tion, &e., are given of the typical species of Amnicola, Bythinella, and 
the new genus teens Similar lldatratione, and a escrip- 
seed gy given of the type (Amnicola lapidaria Say,) upon which the 
atop and the subfamil Pema sing, W u 
Sthee: rage he gives an extended — of the retail Ivins . 
th accurate diagnoses of each s 
a 
biine, wi 
