Mr. W. Thomson on the Dentition of British Pulmonifera. 93 



forms clearly. The last species on my list is Cyclostoma ; but as 

 this belongs to a section of the Pulmonobranchiata differing so 

 widely from that to which the subjects of my preceding remarks 

 belong, I. will not describe it, but merely call attention to the 

 general aspect of its tongue, which much resembles that of some 

 of the fluviatile Pectinibranchiates ; to these species the Cyclo- 

 stoma presents some analogy, in being unisexual, and operculated, 

 in having but two tentacles, with its eyes placed at their base on 

 their outer sides, and in being a vegetable feeder. 



It will be desirable, perhaps, before I conclude this paper, 

 that I should give some idea of the number of teeth in a trans- 

 verse or horizontal row in a few species, together with the number 

 of those rows upon the tongue, and the whole number of teeth 

 on that organ. And to this I propose to add also, the actual 

 size of the individual teeth of one or two species, to show their 

 minuteness. 



Arion ater 



Limax maximus. 

 carinatus . 



Vitrina pellucida 



Helix aspersa 



nemoralis .. 



Pomatia 



obvoluta .. 



lapicida 



pulchella . . 



Cantiana .. 



fulva 



concmna .. 



Pisana 



caperata . 



ericetorum 



Zonites alliarius . 



cellarius . 



nitidulus . 



Succinea putris . . . 

 Bulimus obseurus 

 acutus 



Zua lubrica . . . , 

 Pupa juniperi 

 Balsea perversa . 

 Clausilia bidens . 

 nigricans 



Limnaeus stagnalis. 

 Ancylus fluviatilis . 

 Velletia lacustris . 



Number of 

 teeth oa 

 tongue. 



17,600 



26,800 



8,000 



7,500 



14,175 



13,500 



21,000 



15,300 



12,000 



1,950 



10,000 



3,150 



5,000 



8,400 



4,500 



6,900 



1,125 



945 



3,575 



3,250 



6,600 



3,700 



3,200 



4,000 



5,200 



6,000 



3,600 



12,100 



9,000 



3,000 



It will I think be readily conceded, from a glance at this table, 



