INVERTEBRATES. 117 



AVICULOPECTEN MAZONENSIS. (sp. nOV.) 

 PL XXII. Pig. 9. 



Shell rather below medium size, ovate, slightty inequilateral; 

 left valve moderately convex, the greatest convexity being about 

 2 / 5 the distance from the hinge line to the cardinal border. 



Hinge line straight, beak depressed, extending slightly bej^ond 

 the hinge line, and situated a little forward of the middle. 

 Ears nearly equal in size, triangular, and marked by about 

 eight radiating costie, much smaller than those on the body of 

 the shell. Anterior lateral border regularly rounded from the 

 base of the~anterior ear to the cardinal border. 



Cardinal border regularly rounded; posterior lateral border 

 nearly straight from the base of the posterior ear to the point 

 where it joins the rounded cardinal border. 



Surface of the left valve ornamented with about thirty rounded 

 costae on the cardinal border, which on the middle of the shell 

 are about as wide as the intervening spaces, but unequal in 

 size. A portion of the cost* becomes obsolete before reaching 

 the hinge line. 



Length of a large individual l 6 /i e inches; breadth about the 

 same; length of hinge line 1 inch. 



Position and locality: Coal Measures, Mazon creek, Grundy 

 county, 111. 



No. 2952 of the Illinois State Museum. 



AVICULOPECTEN HARDINENSIS. (sp. nov.) 



PI. XXII, Figs. 5-5a. 



Shell of medium size, obliquely ovate in form, the length ex- 

 ceeding by about one-tenth the lateral diameter. Basal and 

 lateral margins regularly rounded. 



Left valve moderately convex, beak obtuse, hinge line straight, 

 and equal in length to about four-fifths of the greatest lateral 

 diameter. Anterior ear rather narrow, triangular, and sharply 

 defined from the lateral border. Posterior ear broken away. 



Test thin and ornamented with longitudinal rays of which 

 about four to five may be counted on the basal border in the 

 space of one-fourth of an inch. The longitudinal rays are 



