THE NAUTILUS. 93 



Draparnaud had first separated the marine round-mouthed shells 

 from their supposed terrestrial congeners, which led Lamarck to 

 erect his genus Delphinuhi for the reception of some of tlie marine 

 forms, and later Paludina for others, which genus was substituted for 

 his own Vivipara. Helicina although proposed as a genus hy Lam- 

 arck was not grouped by him near the cyclostomous genera. Its 

 operculiferous character was known, hut in spite of this fact its 

 position was assigned in the family of the Colimaces (Pulmonifera), 

 amongst the helices, bulimi and pupas. Ferussac had first recog- 

 nized that the genera Helicina and Cyrlostoma were closely related, 

 and had, in deference to their similar breathing organization, placed 

 them at the end of the air-breathing gasteropods. 



Reeve united Pupina, Truncate/la, Cyclostoma, and Helicina in the 

 single family Cyclostomacea. Menke as early as 1828 appears to 

 have separated the operculate shells into two families, typified by 

 Helicina and Cyclosfoma. Dr. Gray (1842) first pointed out the 

 significant morphological distinction between Cyrlostoma and He- 

 licina, and assigned to the family Helicinidae the three genera 

 Helicina, Lucidclla, and Alcadia, while Swainson (1840) had 

 grouped together Helicina Lam., Pachyloma Swains., Oligyra Say, 

 Trochatella Swains., and Lucidella Swains. In the monograph 

 (184G) in Kuster's Conchylien Cabinet upon "Die gedeckelten 

 Lungenschnecken," by L. Pfeiffer, the family Helicinacea was re- 

 garded as composed of the genera Trochatella Swains., Lucidella 

 Swains., Helicina Lam., and the family Cyclostomacea of Cyclosfoma 

 Lam., C/ioanopoma Pfr., Cyclophorus Montf., Leploma Pfr., Megalo- 

 mastoma Guilding, Pupina Vignard, Cnllia Gray, Pumalias Studer, 

 Aulopoma Trosch., Craspedopoma Pfr., Myxostoma Trosch., Ptero- 

 cyclas Bens., Acicula Hartmann, Geomelania Pfr., Hydrocena 

 Parreyss. 



The generic divisions thus slowly evolved had been largely based 

 upon the characters of the opercula, and it seems that the credit of 

 emphasizing this feature was due to J. E. Gray, who in 1825 pub- 

 lished in the Zoological Journal and Philosophical Transactions the 

 results of his observations on their structure, formation and growth, 

 and insisted on their affording " characters for the division of families 

 and genera as the shell of the gasteropods themselves, and that to 

 neglect them in the description of the genus or species is quite as 

 rational as to describe only the single valve of a bivalve shell." The 



