CYCLOSTOMA. 



and West Indies, and in the Islands of the South Seas ; 

 and though we have received a great assemblage of vari- 

 ous shells from North America, we have not a single 

 Cyclostoma among them. Of fossil species there are very 

 few ; the C. Mumia, which occurs in some of the upper 

 tertiary beds in the vicinity of Paris, is the only decided 

 fossil species we are acquainted with ; for though Lamarck 

 mentions seven or eight fossil species, it is more than 

 probable that most of them are Valvatse. 



Lamarck has described twenty-six recent species, which 

 are probably true Cyclostomata, for his C. Mumia is, as 

 he afterwards states, is only found in a fossil state, and 

 his C. truncatulum, which he has adopted from Drapar- 

 naud, is not a Cyclostoma. I am acquainted with more 

 than eighty species, but there are several of Lamarck's 

 which I cannot recognize, namely, C, ambiguum, C. de- 

 cussatum, C. lineolatum, C. mammillare, C, orbella, and 

 C. multilahre. I have represented several species showing 

 as great diversity of form as I know to exist among the 

 shells composing the Genus. One of these is nearly dis- 

 coid, and shaped very much like a Planorbis, another is 

 nearly cylindrical, one has an undulated fringed margin 

 to the aperture, and another has no reflected margin. 



