INSTITUTE OF SCIENCE, PHILADELPHIA. 427 



margin may assume an imbricated form; interior smooth, the margin crenu- 

 late in the young, in the full-grown rather sharply and coarsely denticulate 

 radially ; foraminal callus spade-shaped, slightly dinted behind. Alt. 7; Ion. 

 15 ; diam. 9.5 mm. 



This species much resembles F. alternata Say, but seems more depressed 

 and elongated, and has the foramen habitually more anterior. It does not seem 

 to attain so large a size as the recent specimens of alternata. It is undoubt- 

 edly the forerunner of that species. 



Fissuridea caloosaensis n. s. 

 Plate 21, figure 6. 



Pliocene of the Caloosahatchie beds and Shell Creek, Florida, Dall and 

 Willcox. 



Shell large, depressed, with a link-shaped foramen which sometimes is 

 distinctly keyhole-shaped ; radiately sculptured with feeble, shallow, rather 

 narrow sulci, between which the lines of growth are convexly looped toward 

 the apex of the shell, and by regularly-spaced, rather close-set, impressed 

 lines give the effect of being imbricated toward the foramen ; under the lens 

 the sculpture has the effect of combed wool, the rippled fibres lying in har- 

 mony with the incremental lines ; interior smooth, the muscular impression 

 strong, the foraminal callus having the outline of a Gothic window ; its outer 

 margin somewhat fimbriated or irregularly denticulated; margin of the shell 

 feebly crenulated. Alt. 12.O; max. diam. 40.0 ; Ion. 50.0 mm. 



The specimen figured has been more or less decorticated. From a frag- 

 ment collected by Mr. Willcox at Shell Creek the normal appearance of the 

 sculpture has been described ; there are no analogous recent species in the 

 region. The nearest approach to it in the matter of surface-sculpture among 

 recent species seems to be Clypidella pustula. 



Fissuridea carditella n. s. 

 Plate 21, figure ir. 



Pliocene of the Caloosahatchie beds, Dall. 



Shell elongate-ovate, rather depressed, the foramen in the anterior half, 

 which is somewhat narrower than the posterior portion ; foramen elongated, 

 keyhole-shaped ; sculpture prominent and intricate, comprising strong radi- 

 ating ribs, with narrower interspaces and much smaller intercalary riblets, 

 which are crossed by sub-laminar concentric ridges, more distant near the 

 apex, more crowded toward the base, and rather regularly spaced ; near the 

 apex is reticulated, with the radials predominant, but below it becomes more 

 crowded ; the intersections above are marked by transverse nodules, which 

 gradually, as they advance toward the base, become more developed and 

 hollowed basally, until near the margin, in a perfect, well-developed specimen, 

 the appearance of the ribs suggests little heart-shaped cups, fitting partly into 



