167 



A SYNOPSIS OF THE RECENT AND TERTIARY FRESHWATER 

 MOLLUSC A OF THE CALIFORNIAN PROVINCE, BASED UPON 

 AN ONTOGENETIC CLASSIFICATION. 



{Concluded fi-om X). 165.) 



By Harold Hannibal. 



Bead 10th May, 1912. 



PLATES VII- VIII. 



Superfamily MELANOIDE^ (Swainsou), 1840. 



Thk Melanoiclefe include several families of cerithiform operculates 

 inhabiting the marine littoral zone, estuaries, amphibious situations 

 near the sea, and purely fresh waters, among which may be noted the 

 Melaniidge, Swainson, 1840, Turritellidae, H. & A. Adams, 1854, 

 Cerithiidae, H. & A. Adams, 1854, Melanopsidae (H. & A. Adams), 

 1854, Pleuroceridse, Fisclier, 1887, and Ellipstomidae, n.fam. In 

 few other groups of Gastropods is the classification more involved 

 than among the brackish and freshwater Melanoids ; species but 

 distantly related so closely resemble one another that the only 

 safe criterion by which to distinguish them lies in the anatomy. 

 Even in the following family, however, represented in fully two- 

 thirds of the streams of the United States, the internal characters 

 have not been sufficientlj' described to offer a clue to what constitutes 

 generic differences. 



Family PLEUROCERID^, Fischer, 1887. 



Shell of variable size, fusiform or conical, covered with a greenish 

 or tawny epidermis frequently marked by darker spiral bands, whorls 

 more or less appressed, sutures but little impressed, aperture in its 

 simplest form normal, the outer lip sinuate, slightly retracted and 

 produced below, in the more specialized forms with an elongate 

 fusiform canal or sutural pleurotomariform cleft ; animal oviparous, 

 mantle-margin simple, operculum horny and concentric; habitat 

 chiefly fluviatile. 



Two stages or sub-families depending chiefly on the modification of 

 the apertui'e are recognizable as follows : — 



Sub-family PLEUROCERIN^, s.s. 



Shell melaniform, periphery generally smooth and rounded, aperture 

 simple, the outer lip sinuate, slightly retracted and produced below. 

 Genera, Pleurocera, s.s., Amhloxus, Gyrotoma, sub-gen. Goniobasts. 



Sub-family GYROTOMIN^, n.sub-fam. 



Shell not typically melaniform, whorls more or less peripherally 

 carinate and nodose or nodose-spinous, aperture produced below into 

 a fu.siform canal, or retracted above into a sutural cleft ; Pleiirocerince 

 stage passed during adolescence. 



VOL. X. — OCTOBER, 1912. 12 



