HANNIBAL: CALIFOKNIAN FRESHWATER MOLLUSCA. 179 



Little Falls, Washington ; bluffs along Olequa Creek above shoals 

 il 2 miles north of town (types) ; at shoals H miles north of town ; 

 I bend half a mile south of town (H. Hannibal). 



I Genus Gyrotoma, Shuttleworth. 



' Schizostoma, Lea, 1842 [Melania {Schizostoma) excisa, Lea), not 

 Schizostoma, Bronn, 1835 ; Gyrotoma, Shuttleworth, 1845 

 (C ovoidea, Shutt. = i/. excim. Lea); ' JUelatoma, Swainson,' 

 Gray, 1847; SchizocJiilits, Lea, 1852 (J/, excisa, Lea, by sub- 

 stitution), preocc. in Coleoptera ; Aphella, ' Mighels MS.,' 

 Anthony, 1860 (no described species cited), in synonymy. 



Sub-genus Goniobasis (Lea). 



, Melania (sp.), Conrad, 1834 (J/, olivula, Conr.) ; Megara (sp.), H. & 

 A. Adams, 1854 (J/, olivula, Conv.) ; Go7iiohasis {pars), Lea, 1862 

 (G. oscidata. Lea = M. olivula, Conr.); MacroUmen, Lea, 1862 



& {Melania {Bfacrolimen) Shoivaltherii, Lea = M. olivula, Conr.). 



Type, Melania olivula, Conrad.^ 



Sub-genus Gotiiobasis. Shell rather small, averaging 20 mm. in 

 altitude, solid, regularly conic, whorls appressed and normally smooth, 

 with a rounded periphery, apei'ture ovate-elliptical, columella curved, 

 outer lip barely sinuate, produced below, and slightly retracted above ; 

 habitat streams. 



Sub-genus Gyrotoma, s.s. Shell as in Goniobasis, but the whorls 

 sub-nodose below the suture, outer lip sinuate, terminating above in 

 a sutural pleurotomariform cleft; Goniobasis stage passed during early 

 adolescence ; habitat streams. 



Gyrotoma embraces two species and two sub-species characteristic 

 of the Gulf States drainage. Two, both sub-species, beloi:^g to typical 

 Gyrotoma, characterized by a remarkable pleurotomariform cleft 

 analogous to the canal of lo, while the remaining forms group in 

 Goniobasis, in which the more primitive normal character of the 

 aperture is retained. 



On the basis of the aperture alone Goniobasis is liable to be con- 

 fused with Ambloxus, an error already fallen into by several writers, 



' In describing Goniobasis Lea omitted to designate a type. The contents are 

 referable to Vii-ginicus, about sixty-five synonyms ; olivula, eleven 

 synonyms ; plicifcrus, two synonyms, etc. Some synonym of Yirginicus 

 would be the natural choice, but Lea expressly stated that Virginicus itself 

 was to be retained in Melania for the time being, hence it cannot be 

 regarded as a species available to become the type of the present group, 

 and thus saves the name from falling into the synonymy of A)iibloxHS. 

 Lea stated further that the genus might be divided into two sections, of 

 which the first was to include the conical species (i.e. olivula), and the 

 second the fusiform (i.e. Virginicus and pliciferus). The first species 

 named is G. osculata, a synonym of olivula, which may be accepted since 

 it constitutes the nearest approach to Lea's original intentions, regardless 

 of what later writers have attempted to do with the name. The earlier 

 Megara of the Adams was apparently intended for this same group, and, 

 judging by the contents, would be a preferable name. However, it 

 includes the monotype of the prior genus Plcurocera, and is unavailable. 



