INSTITUTE OF SCIENCE, PHILADELPHIA. 339 



Amnicola omphalotropis Pilsbiy, n. s. 

 Plate 2r, figure 13. 



Pliocene marls of the Caloosahatcliie and M}'akka Rivers, Florida, Dall 

 and Willcox. 



" Shell globose-turbinate, composed of four very convex whorls ; smooth 

 except for almost imperceptible lines of growth; apex obtuse ; suture very 

 deeply impressed between the last two whorls ; aperture round-ovate, very 

 little higher than wide ; 'scarcely angulate above; peristome thin, continuous, 

 in contact with the body-whorl above the umbilicus; columellar lip not ex- 

 panded or reflected, excavated and concave; umbilicus rather narrow, conspic- 

 uously excavated and bounded by an elevated carina. Alt. of two specimens, 

 A, 2.5 ; B, 3.0 ; diam. A, 2.0 ; B, 2.2 mm. 



" I have seen but two specimens of this species, which is one of the most 

 distinct known to me in the peculiarly carinated umbilicus and the inner lip, 

 which is so excavated that it lies behind the plane of the outer lip." [H. 

 A. P.] 



After the types were returned by Mr. Pilsbry and the duplicate material 

 scrutinized in the light of his identifications, several other specimens were 

 found, including one from the Upper Pliocene of the Myakka River. All 

 agree very well in the characters assigned to the species, though the umbili- 

 cus differs somewhat in size. 



Subfamily RISSOIN^. 



Genus RISSOA Fr^minville. 



Subgenus Rissoa s. s. 



Rissoa lipeus n. s. 



Plate 20, figure S b. 



Pliocene marl of the Caloosahatchie, one specimen, Dall ; living in the 

 lagoon at Watling Island, Bahamas, Dr. Brown. 



Shell small, plump, with a rather obtuse apex and four and a half inflated 

 whorls; apical whorls smooth, later ones sculptured with two fine, elevated 

 spiral lines with wider interspaces at the periphery and five or six more on the 

 rounded base, becoming somewhat more adjacent toward the pillar; these are 

 crossed by numerous fine, elevated, rather distant threads, beginning at the 

 suture and becoming obsolete after passing over the periphery ; aperture 

 rounded, slightly interrupted by the curve of the body ; margin slightly 

 thickened, pillar-lip arched, with no umbilical chink behind it; edge of the 

 aperture not oblique or sinuous. Alt. 1.3 ; max. diam. 0.8 mm. 



The recent specimen is translucent, and differs only by having one or t\\ o 

 more elevated lines between the periphery and the suture on the last whorl. 



