274 PROCEEDINGS OF THE ACADEMY OP 



large oriental species, is of little value, as he commences the genus Planorbis 

 with cornuarietis, a discoid Ampullaria. 



Conchologists of good repute, as H.-A. Adams, Rrot, Carpenter, Deshayes, 

 Gould, and Lea, continue to place the two groups under the same family name 

 of Melanidae (d'Orbigny) or its equivalent, which is much like uniting Patella, 

 Loltia, and Ancylus, because they have analogous shells. The uncertain posi- 

 tion which these groups hold is apparent in the paper of Mr. Gill, in the Proceed. 

 Acad. Nat. Sci. for Feb., 1863. He there includes the Melaniidae in his " Synop- 

 sis of the families of Pectinibranchiates represented in the fresh-water streams of 

 North America," although he admits (note under Amnicolidae) that they " have 

 not a fringed mantle, and consequently belong to a different group " from the 

 "true Melanians." How then can they be Melaniidae? Of this group he 

 forms " a peculiar ss^family, Ceraphasiinse." Prom his heterogeneous Mela- 

 niidae he rejects certain forms, including Melanopsis and Pirena (probably P. 

 atra (Linn.) and P.fluminea (Gmel.,) lo form a family Melanopidee (and also a 

 subfamily Melanopinae,) to which his Cera(Ceri- ?)phasiinae should belong, as 

 Melanopsis seems to have a simple mantle ; apparently leaving Pirena aurita 

 in his North American Melaniidae. Mr. Carpenter (Smithsonian Report for 

 I860,) not only unites the oriental and North American species, but he assigns 

 a fringed mantle to the latter. 



In the Iconographic Encyc, I placed Melaniidae (the American form) at the 

 head of the Ctenobranchia, followed by Cerithiidae (including the oriental Me- 

 laniae,) Vermetidae, Trochidae, &c. Melania proper, with a festooned mantle, 

 seems to form a subfamily Melanianae of the family Cerithiidae, and the follow- 

 ing species are examples : 



M. celebensis Quoy, Astrolabe, p. 152, pi. 56, f. 28. 

 M. costata Quoy, " p. 155, " f. 36. 



M. cybele Gould, Am. Ex. Exp., p. 132, fig. 1546. 



Virginia is given as the locality of M. fuscala Born, (Helix) Desh. Lam. 

 8,436, which is probably an error. Of Lamarck's sixteen recent species, M. 

 (Pleur.) carinifera is the only one from North America, and Say's M. {Pleur.) 

 depygis is the only one among the twenty added by Deshayes. 



Rafinesque proposed three genera of this fluviatile family, Strepbma, Pleu- 

 rocera and Leptoxis. The last was subsequently described as Anculosa Say, 

 the first as Ceriphasia Swainson, (adopted by H.-A. Adams,) and Trypanosoma 

 Lea, leaving Pleurocera for the varied forms constituting the remainder. But 

 from this remainder I separated Lithasia for shells like Mel. nupera; and Angi- 

 trema for the form including Mel. armigera, which leaves Pleurocera about 

 equivalent to Goniobasis Lea, and to several of the genera proposed by H.-A. 

 Adams, as Melasma, Elirnia, Juga. Thus Juga includes {Pleur.) Virginica Say, 

 (inadvertently placed under Ceriphasia also,) whilst Rafinesque's Pleurocera 

 turricula is a slender shell, like {PL) acuta Lea, or exilis Hald. 



I now propose that Strepbma and Pleurocera shall replace their synonyms, 

 the former as a genus, the latter as a subgenus in the family Strepomatidte. 

 The groups of Messrs. H.-A. Adams often indicate merely sections ; and sec- 

 tional names given as generic are scientifically erroneous, because they erect 

 certain species iato genera and subgenera only when they belong to extensive 

 groups, requiring numerous specific names, whilst the same amount of charac- 

 ter goes for nothing in groups which have but few species. 



All the species of Strepomatidae which I have examined living (including lo) 

 have the mantle simple and the opercle subspiral. This is the case with Stre- 

 poma canaliculata (Say,) the type of the first division of " Melania " in Dr. Brot's 

 admirable Catalogue. . . . des M61aniens, Geneve, 1862. In some species of 

 Leptoxis the adult opercle seems to have a different structure, but this arises 

 from erosion of the earlier subspiral portion, as may be ascertained by compa- 

 ring the different ages. 



[Sept. 



