336 TRANSACTIONS OF THE WAGNER FREE 



the spire more elevated and the shoulder narrower and more sloping than 

 in the A. depressa Say. 



Family RISSOID^. 



Subfamily HYDROBIIN^. 



While it is possible that future researches may render it necessary to 

 separate Rissoina as a separate family from that including Rissoa, Cingula and 

 Hydrobia, it does not seem to be established that sufficient anatomical charac- 

 ters exist to render it advisable to establish a family for Hydrobia and its allies 

 as opposed to the marine Rissoidce. 



Genus HYDROBIA Hartmann. 



It is, of course, impossible to determine positively the genus of these 

 minute shells from the shell alone. In the Caloosahatchie marls we find the 

 fresh-water mollusks of the ancient lagoons mixed indifferently with the 

 marine forms of the adjacent strand ; either because the former were washed 

 into the sea by the current, or because from time to time the sea crossed the 

 low protective barrier of sand and destroyed the fresh-water animals contained 

 in that particular lagoon and mixed with them its own proper fauna. There- 

 fore, the references of the shells of this family are made on the basis of the 

 general appearance of the shells, and sometimes without a definite knowledge 

 of whether they were fresh, brackish or salt-water denizens. 



Mr. H. A. Pilsbry, of the Academy of Natural Sciences, being engaged 

 on a monograph of the American HydrobiincE, in conjunction with Prof Chas. 

 E. Beecher, of New Haven, I submitted to him the species belonging to this 

 puzzling group, and the following identifications and descriptions were kindly 

 furnished by him : 



Hydrobia amnicoloid.es Pilsbry, n. s. 

 Plate 21, figure 5. 

 Pliocene marls of the Caloosahatchie River, Florida, Dall. 

 " Shell ovate-conic, with elevated spire and minute subacute apex ; whorls 

 slightly more than five, quite convex ; surface apparently smooth and shining, 

 but when viewed under a strong lens it is seen to be sculptured with excess- 

 ively fine spiral incised lines ; aperture ovate, not oblique, angular behind ; 

 peristome obtuse, but not thickened, not perceptibly sinuous, continuous, 

 adnate to the body-whorl above the narrow umbilical perforation ; columellar 

 lip slightly expanded. Alt. 4.5 ; max. diam. 2.8; alt. of aperture 2.2 mm. 



" This species differs from Hydrobia umbilicaia in being larger, less 

 slender, in the narrower umbilicus, obvious spiral striation, and in lacking a 

 peripheral angle. It is not closely allied to any other species, unless it be the 

 'Cingula' minuta of New England, which is about the same length and has 



