274 KANSAS UNIVERSITY SCIENCE BULLETIN. 



Measurements : Length, 1.8 mm.; width, 1.25 mm.; height, 0.5 mm. 



Position and locality : Upper Coal Measures, Iola limestone, 

 Kansas City, Mo. Three specimens. 



This is the smallest described species of the genus. In some re- 

 spects it resembles C. packardi, n. sp., antea, and may possibly be a 

 young form of that species. But in the absence of intermediate 

 forms, and as the specimens seem to be perfectly formed, it is desig- 

 nated as a distinct species. 



Our species also resembles C. jonesianus H. Woodw., but it is 

 much smaller, less tumid, the arrangement of the anterior lobes is 

 different, and the furrow separating the inner and outer forks is much 

 more prominent. 



Analytic Key to the American Species of the Genus Cyclus. 



1. With ribs. Wide, flat margin permarginatus. 



Without ribs 2 



2. Circular or subcircular in outline 3 



Transversely elliptical in outline 4 



Longitudinally elliptical in outline, carapace very small minutus. 



3. Subhemispherical, with narrow, nearly vertical margin communis. 



Disk-shaped, with wide, horizontal margin american u$. 



4. Carapace rather large, surface with lobes and small tubercles. . . . packardi. 



Carapace small ; surface with lobes but no tubercles; fringed 



margin limbatus. 



Alphabetical List of Described Species of the Genus Cyclus, with 



Synonomy. 



Cyclus agnotus von Meyer. 



Hallcyne agnotus von Meyer, 1847. 

 Cyclus agnotus H. Woodw., 1870. 



Cyclus americanus Packard. 



Cyclus americanus Packard, 1885, 188G. 



Cyclus bilobatus H. Woodw. 



Cyclus bilobatus H. Woodw., 1870, 1878. 



Cyclus harknessi H. Woodw. 



Cyelux harknessi H. Woodw., 1870, 1878. 



Cyclus johnsoni II. Woodw. 



Cyclus johnsoni H. Woodw., 1894. 



Cyclus jonesianus H. Woodw. 



Cyclus jonesianus H. Woodw., 1870, 1878, 1891. 



Cyclus laxus von Meyer. 



Halicyne laxus von Meyer, 1847. 

 Cyclus laxus H. Woodw., 1870. 



■ 



Cyclus radialis Phillips. 



Agndstus? radialis Phillips, 1836. 



c</r/^s radialis De Koninck, 1811, 1842; H. Woodw. and Salter, 18G5; 

 II. Woodw., 18G8, 1870, 1894. 



