330 Dr. J. E. Gray on the Teeth of the 



and exotic genera. Dr. Wyman the American genera, and Mr. 

 Thompson, who has described the teeth of many of the English 

 genera and species of this order, have shown these pecuharities, 

 and the alterations which occur in the form of the teeth in dif- 

 ferent parts of the same cross series. 



I have examined the teeth of several of the other exotic ge- 

 nera, and find them quite conformable to those of the European 

 kinds. In general the teeth have a broad, expanded, more or 

 less four-sided, oblong base, with a reflexed tip ; the bases of the 

 teeth in the same series and of the neighbouring series being 

 close together on the lingual band, so as to form a close-set 

 rasp. 



This is the case with the genera Arion, Nanina, Parmacella, 

 Clypeidella (Dussumieri) of Arion id^; Philomycus, Limax, Geo- 

 malactis, Vitrina, Helix, Acavus, Arianta, Vallonia, Iberus, Poly- 

 gyra, Theba, Helicella, Succinea, Bulimus, Partula, Zua, Pupa, 

 Clausilia, Balea, and Achatina of Limacid^ ; Veronicella of 

 VERONiCELLiDiE ; OncMdium of Onchidiad^e ; Auricula, Me- 

 lampus, Alexia, Scarabu^ of Auricuhd^; Lymnea, Amphi- 

 peplea, Bulimus, Physa, Coretus, Segmentina, Ancylus of Lym- 

 NEADiE ; Siphonaria of Siphonariad^ ; and Amphibola of Am- 



PHIBOLID^. 



The only exceptions I have observed are in the genera Testa- 

 cellus and Peronia, and the teeth of these animals are exactly 

 similar. They consist of numerous cross series, each series con- 

 sisting of many teeth, like the other families of the order, but 

 the teeth are far apart, slender, curved, with a blunt, rounded 

 upper and a pointed lower end like a pin, and only attached to 

 the lingual band by a slight process on the inner side of the 

 middle of the tooth. 



This difference in the teeth and the peculiar habit of the genus, 

 living as it does on worms, which it swallows whole, induce me 

 to propose to separate the genus Testacellus from the Helicida, 

 and form it into a peculiar family Testacellida, to which Plectro- 

 phorus will probably belong, as it has the same sunken lines on 

 the side of its body from the tentacles to the middle of the back ; 

 and in the same manner I would separate the genus Peronia, 

 which lives on the sea-coast, from the Onchidia, which have the 

 normal teeth of the order. 



The genus Parmacella in Arionidce, and some species of Heli- 

 cella ( = Zonites) and Oleacina in Helicidce, have a much narrower 

 and more elevated recurved apex with a narrow base, and are 

 more distinct from each other in the tongue-membrane, making 

 a kind of transition between the normal teeth of the order and 

 the teeth of the genera Testacellus and Peronia. 



