MOLLUSCA. 241 
long as it is below the surface of the water. These interesting observations 
were made on specimens in the aquarium of the author. 
GASTROPODA. 
Troschel, F. H. Das Gebiss der Sclmecken zur Begriindung 
einer natiirliclien Classification. [The dentition of the Gas- 
tropoda as a base for a natural classification.] Vol. ii. part 1. 
Berlin, 1866 (Decemb. 1865), 4to, pp. 48, with four 
plates. 
We announce with great pleasure the continuation of this 
highly valuable work, which contains the most extensive re- 
searches into the buccal characters of the cephalophorous mol- 
lusks. The first volume, containing the Cephalopoda ^ Ptero- 
poda, Heteropodoj and Gastropoda tamioglossa, was published 
in the years 1856-1863. The introduction to the second 
volume contains, beside a short review of similar essays on classi- 
fication by former authors, a recapitulation of the chief results 
gained by the special investigations recorded in the first 
volume. The author- adopts two primary divisions of Gastro- 
pods, — the monoecian or hermaphroditic, and the dicecian Gas- 
tropods, or those in which the sexes are separate, on different 
individuals. There are some few exceptions, as Valvata^ which 
is really hermaphroditic, but according to all other characters 
its systematic place is among the G. dioecia tcenioglossa, as lias 
been admitted by all authors. The Gastropoda dioecia are 
divided, according to the division of the radula (the so-called 
tongue), into six divisions, viz. : — 1. Tmmoglossa. 2. Toxo^ 
glossa. 3. Rhachiglossa. 4. Ptenoglossa. 5. Rhipidoglossa. 
6. Docoglossa. 
The T(snioglossa, characterized by seven (very rarely three or 
nine) plates in each transverse row of the radula, elevated and 
cutting by their elevated edge, are subdivided thus : — 
I. Rostrum non-retractile. 
1. Lungs : {Aciculacea), Pomatiacea, Cyclotacea^ Cyclostomacea. 
2. Lungs and gills : Ampullariaceaj ? Truncatellacca. 
3. Gills only. 
a. Lateral plates of the radula ribbon-shaped, larger at the outer end : 
ValvatcDj Paludino'^ Pythini< 2 , Lithoylyphi^ Ilydrobia;, Ancylnti, 
I'hiara;, Pachychili, Melanicc, Risso>x^ Littorincc^ Ccrithiacca, Pota- 
mides, Planaxes, 2'urritelles, Possari, H^yjonycidcc. 
h. Lateral plates flat, with long pectinate denticulations : Pedicida- 
riacea, Amphiperasidce \_Omda]. 
c. Lateral plates hook-shaped, more or less distinctly triangulated : 
Vermetacea, Capulaccaj Trichotropidce. 
d. Lateral plates very long and narrow, rather filiform, frequently 
grooved: Onustidcr [P//or«5], Alatn [/S^rowi^ws], Aporrhaidce, 
1865. [voL, II.] ' ' R 
