102 HoGG^ on the Lingual Membrane of MoUusca. 



of the first, Turbo Utoreus of the second, and Patella 

 vulgata of the third." The tongue of Turbo Utoreus 

 (a flat strap-shaped organ of more than two inches long) 

 presents three longitudinal ranges of teeth, which recline 

 backwards, and are set like scales, with very little elevation 

 of their edsjes. In the two outer rows the teeth are sinsle, 

 irregular, crescentic in shape, and set by their convexity. 

 In the middle row the teeth are small, and nearly square in 

 shape. All require a good magnifying power to discover 

 their beautifully reticulated appeai^nce. 



It certainly seems somewhat out of place to class the large 

 and bold Triton with Litorina, since the odontofore of the 

 former diifers so much from that of the latter. The median 

 tooth is armed with strong recurved cusps, the centre one 

 being long, with five more subdued on either side ; the 

 laterals, three in number, are bold,. sickle-shaped teeth, one 

 of which is rather broader than the others. The tongue and 

 spiny buccal plates of Triton are certainly indicative of 

 carnivorous habits. 



Bulimus (Bulhnus oblongus) and Helix differ but little 

 either in their anatomical characters or in that of their denti- 

 tion. The odontofore is a broad band ^vith numerous similar 

 teeth ; the forms, however, of the teeth themselves are very 

 Viiried. Some of the cusps on the teeth of this genus are 

 naturally very pellucid, especially so if the tongue be mounted 

 in balsam, when they frequently escape observation, and 

 owing to this have often been wrongly described. Its man- 

 dible somewhat resembles that of a Cephalopod, and it is 

 worthy of inquiry how far the divisions proposed by zoologists 

 are borne out by this part of the organization. The Bulimi 

 are not numerous in Britain ; it appears there are but three 

 indegenous species known, and one of them, the most 

 common {Bulimus acutus), has been restored by Moquin- 

 Tandon to the genus Helix. 



A study of the odontofore of Cyclostoma elegans (PI. VIII, 

 fig. 5) seems to point to an alliance with Trochus (PI. XI, 

 fig. 48), or some group possessing pleuree. 



In their mode of development Xudibranchs resemble 

 Aplysia, Bulla, and other of these genera. The fry of the 

 latter are almost undistinguishable from those of Tritonia 

 and Doris. The sea-slugs, however, differ in many important 

 particulars from their land congeners. In the first place, 

 although formerly they were thought to be phytivorous, it 

 is noAv certainly known that a greater part of them prefer 

 animal food.* The odontofore would seem to indicate this; 



* Tioschel discovered free sulpliiiric acid in the saliva of Dolium (/alen ; 



