68 Trans. Acad. Sci. of St. Louis. 



being distinguished from that species chiefly by reason of its 

 greater number of radiating striae. In all the collections of 

 Chonopectus sandstone fossils which have been studied in 

 connection with the present investigation, three species of 

 Chonetes have been observed, but only one of these resembles 

 in any degree the description of O. multicosta . From a 

 careful study of the best of these, and comparison with many 

 specimens of C. illinoisensis from the Osage fauna, there 

 seems to be no reason for believing them to be distinct from 

 C. illinoisensis. For the present, therefore, it seems best to 

 consider G. multicosta as a synonym of G. illinoisensis though 

 if the type specimens are found at some future time it may 

 be found to be distinct. In none of the Chonopectus sandstone 

 specimens have the spines been observed, and the specimens 

 themselves are for the most part imperfect. 



Chonetes sp. — Cf . C. geniculata White. 



PI. I. f. 1 6. 



Shell more or less subelliptical in outline, with the hinge- 

 line usually a little shorter than the greatest width of the shell. 

 The pedicle valve strongly convex in the middle, slightly 

 flattened near the cardinal extremities ; three or four oblique 

 spines present along the cardinal margin on each side of the 

 beak. The concavity of the brachial valve much less than 

 the convexity of the pedicle valve, in some individuals 

 it being nearly flat throughout. Surface of each valve 

 marked by eighty to one hundred fine radiating striae. 

 Dimensions of an average specimen: length 5 mm., width 

 7 mm. 



Remarks. G . geniculata^ with which this species may be 

 compared, occurs in abundance in the Louisiana limestone at 

 Louisiana, Missouri, and many specimens from that locality 

 have been examined. The Burlington specimens agree closely 

 with those from Louisiana in general form, but their average 

 size is a little greater, and the radiating striae with which they 

 are marked are much finer, there being only about forty-five 

 or fifty in G. geniculata. In the list of localities for G. 

 geniculata^ given by White with his original description, Bur- 

 lington, Iowa, is recorded with a query, and it was undoubt- 



