22 
Quarterly Journal. 
are named uncini or laterals. It is sometimes broader than 
long, as in Tritonia and Doris , or it is elliptical and spoon¬ 
shaped, as in the Helicidce. In others it is a long nariow 
ribbon, which is either transparent or coloured, and is otten 
many times longer than the animal. In the carnivorous 
animals they say that the radula is forked and fleshy, armed 
with sharp curved teeth and placed at the end ot the 
muscular proboscis, while in the plant-eating tribes it is 
very long and spiny. There is no radula in Junicata , 
and in bivalves it has the form of a cartilaginous styliform 
body enclosed in a sheath, with a tricuspid free cxtiemi y, 
and attached to the sides of the stomach. 
It was Mons. Lov&n who was the first to demonstrate 
that important generic and specific characters may 
derived from a careful examination of this organ, ft is 
not my object to give a r6sur)i6 of the history ot t ns 
subject, or an account of its bibliography, so I will meie y 
say now, that it will be easily studied by a ^ c ^ erc J ,lco ?, 
“ Gray’s Guide to the Systematic Distribution ot Mol usca, 
in the British Museum catalogues. Excellent notes are 
to be found also in Woodward’s “Recent lossil bheUs 
and I would recommend any one who wishes to unaerstan 
the structure of the radula amid air-breathing mollusca to 
study the masterly and philosophical essay of AN • lhompson, 
in the “Annals of Natural History,” for 1851, p. 8(>. 
Dr. F. H. Troschel has recently published an attempt at 
classification of mollusca, founded on the dentition a one. 
His work is not yet complete. It is published at Bei m, 
and is entitled “ Das Gebiss der Sehnecken zur Begrunciung 
einer naturlichen classification untersucht. ^ I he au lor 
divides the sub-kingdom into the following ordeis .— 
1. Campylodonta. . 2. Orthodonta. 3. Heterodonta. lhe 
first he divides into two families the Tamioglossa , 
Rhipidoglossa; the second into Toxoglossa, JjacMglosm , 
Ptenoglossa; the third into Docoglossa.. After having 
studied all the radulas that he had at his disposal the 
author has altered the classification or rather the position 
of many genera. He finds, for instance, that the long 
narrow spinifonn teeth amongst Iantliina brings them 
very near to Acteonidcc and Scalariacea. He thinks, also, 
that the Solariacea should be arranged with the I tenoglossa, 
because the teeth furthest from the centra begin to show 
signs of cusps, and consequently to be sensibly distinct fioin 
