106 TRANS. OF THE ACAD. OF SCIENCE. 



rounded carina; ; succeeding whorl with a single obscure ca- 

 rina, becoming obsolete on the inner whorls ; aperture sub- 

 quadrangular ; umbilicus deep, exhibiting all the volutions. 



The diameter of the largest specimen I have seen of this 

 species is about six lines, but usually it does not exceed four 

 lines. In the most perfect example of this species which has 

 come under my observation the dimensions are : height, 2 

 lines ; width, 3^ lines ; width of umbilicus, H lines. 



This little species is very abundant in the cherty beds of 

 the 3d Magnesian Limestone at a single locality in Ozark 

 county, Missouri. It has not been observed elsewhere in the 

 State. 



Missouri State Collection. 



MURCHISONIA OzARKENSIS, n. Sp. 



Shell small, slender, spiral angle about 15° ; whorls about 

 seven, moderately convex, marked with rather obscure, re- 

 volving carinse, of which there are four or five on the body 

 volution; suture linear, well impressed; aperture elliptical. 



Length, about 5 lines ; width of body whorl, 1\ lines. 



This species occurs somewhat sparingly as silicious casts in 

 rough cellular chert, of the 3d Magnesian Limestone, in Ozark 

 county, Missouri. 



Missouri State Collection. 



MtJRCHISONIA CARINIFERA, n. Sp. 



Shell small, conical ; whorls subangulated, and bearing a 

 rounded, revolving central carinse ; suture distinctly im- 

 pressed. Spiral angle, 17° ; sutural angle, 62°. 



All the specimens found are casts, and in most of them the 

 carina is apparent only in the lower whorls. 



Resembles 31. perangulata (Hall), but the mesial band is 

 not double as in the New-York fossil. 



Occurs with the preceding species. 



Missouri State Collection. 



Rapiiistoma scbplana, n. sp. 



Shell depressed, turbinate ; width rather more than one 

 third the height ; whorls about four, periphery of last whorl 

 sharply anguhited, inner edge obtusely angulated; upper sur- 

 face subplane, with a shallow groove just within the exterior 

 margin ; under surface convex ; umbilicus small ; aperture 

 transverse, subtrigonal. 



Width, 42 lines; height, 3 lines. 



This shell resembles JZ. planistria, variety parva (Hall), 

 a species of the Chazy Limestone of New- York, but is more 



