DESCRIPTION OF SPECIES BRACHIOPODA 299 



Chonetes shuniardiana De Kon., with which C. illinoisensis has some- 

 times been compared, has not come under the observation of the writer, 

 but it is a much more finely marked species, with about 12 costse in the 

 space of one millimeter. 



The specimens in the Fern Glen fauna which are identified as 0. illi- 

 noisensis are usually somewhat larger than the average sized specimens 

 in the Burlington limestone, although none of them are as large as the 

 largest of the Burlington specimens. They agree closely with the Bur- 

 lington shells in the size and number of costse and in the general outline 

 of the shell, although they sometimes appear to be proportionally a little 

 wider because of the slight crushing of the shell which has often taken 

 place. 



CHONETES LOGAN I N. & P. 



Plate 12, figures 12-13 



1855. Chonetes logani N. & P., Journal of the Academy of Natural Science of 

 Philadelphia (2), volume 3, page 30, plate 2, figures 12a-b. 



1892. Chonetes logani H. & C, Paleontology of New York, volume 8, part 1, 

 plate 16, figure 25. 



Description. — Shell small, wider than long, the greatest width along 

 the hinge line, cardinal extremities angular. Pedicle valve strongly con- 

 vex or inflated in the central portion, compressed toward the cardinal 

 angles to form small auriculations, without mesial sinus ; surface marked 

 by from 35 to 45 rounded, bifurcating costas crossed by raised, concentric 

 markings which are entirely or nearly obsolete in the furrows between 

 the ribs; cardinal area narrow, the cardinal margin marked by two or 

 sometimes three spine bases. Brachial valve deeply concave, following 

 closely the curvature of the opposite valve. 



The dimensions of an average example are: Width, 11 millimeters; 

 length, 7.5 millimeters; convexity, 4 millimeters. 



Remarks. — This is not a common species in the Fern Glen fauna, but 

 most of the specimens observed are more or less nearly complete. The 

 species can be easily distinguished from the associated C. illinoisensis by 

 reason of its smaller size, its greater convexity, and its stronger, rugose, 

 radiating costae. 



PRODUCTUS FERNGLENENSIS n. sp. 



Plate 12, figures 14-17 



Description. — Shell of medium size, a little wider than long, except in 

 very old and much produced individuals, the hinge line a little shorter 

 than the greatest width of the shell, cardinal extremities with small 



