92 THE NAUTILUS. 



Among this unassorted assemblage were placed marine, fluviatile 

 and terrestrial shells. Later Lamarck withdrew the marine and 

 fluviatile shells, and in 1819 he limited the genus Cyelostoma to 

 terrestrial species. 



In 1829 the Rev. M. G. Berkeley described the anatomical struct- 

 ure of Cyelostoma elegnns (Zoological Journal, vol. iv, p. 278), and 

 alluded to the operculum as " ovate spiral, calcareous." Tliis de- 

 scription was, up to that time, the most extended and accurate that 

 had been published, of the soft parts of the animal of this group of 

 mollusca. 



In the second edition of the Hisloire Naturelle des Animaux sons 

 Vertebres, edited by Deshayes and Milne-Edwards (1838), the 

 diagnosis is Testa varia ; anfraclibus cylindraceis. Apertura circin- 

 ata, regidaris : marginibus orbicidatim cunnexis, aetute patent i-reflexis. 

 Operculum. 



In his observations Lamarck alludes to the similarly circular and 

 entire margins of the aperture of Paludina, but remarks that in adult 

 cyclostomas the edge of the peristome is reflected, whereas in 

 Paludina and generally in fluviatile shells these edges are sharp and 

 plain. 



The comments of the editors exhibit the diversity of views then 

 held by naturalists as to the affinities of these interesting sliells ; 

 some gave full weight to the fact of their aerial respiration and 

 grouped them in a special order, in which their manner of respira- 

 tion, their terrestrial habit, and the possession of an operculum 

 formed distinguishing or separative features ; while others consider- 

 ing their respiration unimportant, dwelt upon morphological re- 

 semblances to Turbo, Troclais and Scalaria. These resemblances 

 were the two tentacles, the absence of eye-stalks, the eyes placed at 

 the base of the tentacles, and the respiration anteriorly open. This 

 latter view was advocated by Cuvier. It was further emphasized by 

 their unisexual nature, and in the armature of their lingual ribbon, 

 which however rather coincides with that of pectinibranchiate gas- 

 teropods. Milne-Edwards and Deshayes regarded the cyclostomas 

 as terrestrial Turbos breathing air. 



Amongst the forty-five species enumerated by Lamarck in 1838, 

 are representatives of the genera Pterocyclas, Cycloplionts, Choano- 

 poma, Tudora, Chondropoma, Helicina, Cyclotus, Otopoma, Lepto- 

 poma, Truncatella, Megalomastoma, and Realia. 



