108 Trans. Acad. Sci. of St. Louis. 



Strophostylus bivolve (W. & W.). 



PI. V. f. 4-5. 



Shell of medium size, composed of about two closely coiled 

 volutions, with the spire scarcely elevated above the outer 

 one. The inner volution small, the outer one more rapidly 

 expanding, becoming ventricose. Cross section of the outer 

 volution ovate, narrowest at the inner margin. Surface 

 marked by fine transverse lines of growth, parallel to the 

 margin of the aperture. Greatest diameter of the shell 19 

 mm., height of aperture, 11 m., width of aperture, 11 mm. 



Remarks. This specimen is included among the types of 

 S. bivolve in the University of Michigan collection, the three 

 other specimens being from a higher horizon. The specimen 

 believed to be the actual type from which original description 

 was made, and which has been illustrated by Keyes,* is one of 

 the other specimens. This single specimen observed from the 

 Chonopectus sandstone, differs from all the others in the 

 much greater size of the inner volution of the shell, and con- 

 sequently in the less rapid expansion of the outer volution. 

 It is possible that it should be considered as a distinct species, 

 but it is desirable that additional specimens should first be ex- 

 amined in order to determine the constancy of its characters. 



Sphaerodoma pinguis (Win.). 



PL vi. f.l-2. 



Shell subglobular, spire short and tapering rapidly, three 

 greatly overlapping volutions recognizable in the type speci- 

 men, suture moderately impressed. The body volution ven- 

 tricose, broadest in the middle ; the aperture ovate, its longer 

 axis forming an angle of 27° with the axis of the shell, acute 

 posteriorly, rounded anteriorly ; inner lip flattened. Surface 

 marked by faint, transverse striae of growth. Height of the 

 shell, 47 mm., length of aperture, 37 mm., width of aperture, 

 25 mm., spiral angle, 85°. 



Naticopsis depressa Win. 

 Pi. VI. f. 3-4. 

 Shell small, narrowly umbilicate, the type specimen with 



* Mo. Geol. Surv. 5. pi. 53, f. 4. 



