INSTITUTE OF SCIENCE, PHILADELPHIA. 389 



spirally threaded with articulated light and dark color-markings on the 

 threads. Some specimens show a fine, sharp secondary striation, but this is 

 not a constant character. It is not impossible that Monodonta Kialnvahensis 

 of Tuomey and Holmes is merely a rather elevated specimen of this species, 

 but I have had no opportunity to compare with the type. 



Ohlorostoma (exoletum var. ?) limatum Dall. 



Older Miocene of the lower bed, at Alum Bluff, and one mile below 

 Bailey's Ferry on the Chipola River, Florida. 



This, which may prove with more material to be a distinct species, differs 

 from C. exoletum by its nearly smooth surface, and, in the young, by having 

 one or two keels near the periphery, which are the more prominent from the 

 general smoothness of the shell ; and a somewhat smaller umbilicus bounded 

 by a strongly annulated or transversely wrinkled rib ; the shell is on the 

 whole more depressed than exoletum, but has similar, though fewer, lines, 

 articulated with dark and light color. The most nearly adult specimen 

 measures 7 mm. high by about 9.5 mm. in greatest diameter. It is a variation 

 from exoletum in the direction of C.fasciatum Born. 



Ohlorostoma (Omphalius) fasciatum Born. 

 Trochiis fasciatus Born, Mus. Caes. Vind. p. 331, pi. 12, figs. 3, 4. 



Pliocene of the Caloosahatchie beds, Willcox and Dall ; recent in the 

 Antilles, the Florida Keys, and the west coast of the Gulf of Mexico as far 

 north as Texas. 



This elegant shell appears well developed, and with its color-pattern 

 almost perfectly preserved, in the Caloosahatchie Pliocene. A feature not com- 

 monly noted in the descriptions, yet frequently conspicuous in the young, 

 especially when fossil, is the deep grooving parallel with the umbilical ribs. 

 Something of this sort is occasionally present in the young of all the species 

 of Oviphalius, though the grooving varies a good deal in intensity, and may be 

 entirely absent. When present in force, it would be just the thing to entrap 

 some inexperienced student into the creation of a " new genus." 



Genus GIBBULA Risso. 



Gibbula americana n. s. 



Plate 22, figure 32. 



Chesapeake Mjocene of Duplin County, North Carolina, Burns. 



Shell small, turbinate, of five whorls ; nucleus small, smooth ; whorls 



sculptured spirally by (on the last whorl about a dozen) larger primaiy and 



smaller intercalary rounded threads, and by numerous regularly-spaced, rather 



close-set, elevated incremental lines, most conspicuous in the interspaces ; one 



or two of the primaries near the periphery are slightly larger than the rest, 



otherwise the whorls are evenly rounded ; sutui'e distinct ; umbilicus small, 



