24 Observations on the Terrestrial 



The following outline represents the buccal plat.e of Y. pulchella, 



^;rf^__^-j7 {Fiff. 60, from Moquin Tanclon,) this diifers con- 



(Fig. 60.) siderably from V. minuta, for in the last named species 



we have a broad narrow plate with the cutting edge not elevated 



or produced in the centre as in V. pulchella, but straight and 



finely notched by the perpendicular strije. 



The three following species differ so greatly from ^.each other 

 in the shell, lingual dentition, buccal plate, and proportion and 

 form of the extended animal, that I consider it a less violation of 

 their natural characters to separate them under distinct generic 

 names, than to unite them under one common title. In Helicodis- 

 cus (nov. gen.) we have a peculiar structure of the shell, buccal 

 plate, dentition, and form of the head. In Planogyi-a (nov. gen.) 

 we have again certain diffei'ences in the shell, buccal plate and 

 dentition, which make it distinct from all other genera herein 

 described. The habits of the si^ecies forming this genus are 

 nearly aquatic. In Strobila (nov. gen.) we see such profound 

 differences in the shell combined with other peculiarities, that we 

 are forced to place this species also under a distinct generic title. 



Planogyra asteriscus, Morse. {Fig. 50.) 



This species first discovered at Bethel, Maine, has since been 



found at Gorham, Maine, and on the Kennebec River, also at 



Salem, Mass., on the Hudson River, 



N". Y., and at Gaspe, Canada East. 



I. A. Lapham has it also from the 



northern shores of Lake Superior ; it 



seems by this to be widely distribu- 



[Fig. 50.) ted; it must however be regarded as 



a species of rare occurrence. In the only two places where I 



have found them, the ground was very wet and boggy; they 



occurred abundantly however, and the intermixture of coniferous 



trees appear to produce no disturbance to their 



pei-petuation and inci-ease. The animal is very 



translucent, body bluish white, head, neck and 



tentacles mottled with bluish black in streaks and 



dots ; disk yellowish white. (Fig. 51.) The shell 

 Fig. 51. 



