INSTITUTE OF SCIENCE, PHILADELPHIA. 95 



the Chipola River in N. W. Florida. Also in the Orbitolitic rock overlying 

 the silex-beds about Tampa. 



The Claiborne species C. fusoides Lea is distinguishable from the Vicks- 

 burg form by its shorter and plumper form, smaller average size and the im- 

 pressed line in front of the suture. All the species I have seen from the silex- 

 beds are of one species, which is proportionally longer and smoother when 

 adult than in youth. The recent species C. Blakeana Dall is closely related 

 to it, but is still smoother and with shorter spire. Both the recent and the 

 fossil forms are very variable in form and sculpture, but they represent with- 

 out doubt the successive terms of an hereditary series. The specimen figured 

 is a siliceous pseudomorph from Ballast Point which does not show the spiral 

 lines, but their traces can be perceived under a glass, and on some other speci- 

 mens they are conspicuous. Specimens reach 17.5 mm. in length. 



Genus MITROMORPHA Adams. 



Mitromorpha cincta n. s. 



Plate 3, figure 6. 



Caloosahatchie beds, on the Caloosahatchie River, rare. 



Shell small, six-whorled, subfusiform, with a blunt, smooth nucleus; 

 transverse sculpture only of faint incremental lines; spiral sculpture of promi- 

 nent keels with wider interspaces, about four keels appearing between the 

 inconspicuous sutures ; whorls rather flattish, the periphery of the last whorl 

 subangulate in the young ; mouth narrow, more than half the length of the 

 shell; outer lip crenulated by the sculpture when thin, simple in the adult; 

 inner lip nearly straight, with a very obscure ridge on the middle of the pillar, 

 deep in the throat in the adult. Lon. of shell 7.25 ; max. lat. 3.0 mm. 



This plain and simple little species is more slender and has more distant 

 spirals than the recent M. dormitor Sby., there are no granulations on the spirals 

 nor the prominent nodules on the pillar such as characterize the recent M. 

 biplicata Dall. 



The ridge on the pillar is not prominent enough for a plait, but rather like 

 an extra deposit of callus. 



Mitromorpha pygmsea Dall. 



Plate 10, figure 3. 

 Shell small, fusiform, with five whorls, of which one and a half are nuclear ; 

 nucleus smooth, polished, rapidly enlarging, the initiatory part being quite 

 small ; spiral sculpture of strong, squarish threads, with wider, channelled in- 

 terspaces ; there are four threads between the sutures ; transverse sculpture of 

 obscure incremental lines and on the upper whorls of 12-14 rounded "bs, 

 strongest anteriorly, overridden by the anterior threads, but ceasing in front 

 of the posterior thread, by which the suture is made conspicuous ; whorls 

 slightly rounded ; aperture about half the length of the shell, narrow, pointed 



