DESCRIPTION OF SPECIES PELECYPODA 319 



lines of growth which are produced into lamellose extensions, especially 

 toward the cardinal extremities. 



The dimensions of the type specimen, a right valve, are : Height, 34.5 

 millimeters; width, approximately 27 millimeters; length of hinge line 

 on posterior side of beak, 12 millimeters; convexity, approximately 6 

 millimeters. 



Remarks. — This species is based primarily upon a single incomplete 

 right valve, which does not exhibit all the characters as well as might be 

 desired, and the dimensions given above, in some cases at least, are liable 

 to be in error because of the distortion of the specimen. A fragment of 

 another example, which possibly belongs to the same species, represents 

 a much larger shell with much more strongly developed concentric 

 growth lamellae. The species is characterized by its slight obliquity and 

 by the peculiar character of the surface markings. 



CONOCARDIUM sp. undet. 



A few fragments of a shell which seems to be a member of the genus 

 Conocardium have been observed in the Fern Glen fauna, but none of 

 them are perfect enough to allow the species to be identified or described 

 if it is an undescribed form, as is entirely probable. 



GASTROPODA 

 PLATYCERAS PAR ALIUS W. & W. 



Plate 15, figures 17-18 



1862. Platyceras paralium W. & W., Proceedings of the Boston Society of Nat- 

 ural History, volume 8, page 302. 



1894. Capnlus paralius Keyes, Missouri Geological Survey, volume 5, page 174, 

 plate 2, figures la-6. 



Description. — Shell of medium size, more or less carinate, usually 

 closely coiled at the apex through about one somewhat oblique volution, 

 beyond which the body volution becomes free, the sides of the outer volu- 

 tion spreading rather rapidly. Aperture subcircular to subelliptical in 

 outline, but usually subcircular in undistorted shells, the margin more or 

 less denticulate with rounded points and sinuses. Surface of the shell 

 marked by more or less distinct, but sometimes obscure, flattened or de- 

 pressed convex, longitudinal ribs, which are projections of the marginal 

 denticulations and which become more obscure toward the apex of the 

 shell; surface also marked by fine transverse lines, with an occasional 

 stronger line of growth whose direction is parallel with the irregular 

 margin of the shell. 



