270 KANSAS UNIVERSITY SCIENCE BULLETIN. 



Generic Diagnosis of Cyclus De Koninck, 1841. 



Cephalothorax small, disk-shaped to subhemispherical, bilaterally 

 symmetrical, usually with a median ridge posteriorly, circular to el- 

 liptical or oval in outline ; ornamentation consisting of lobes, ribs, 

 "forks," or nodes, often with granules occupying more or less of the 

 surface of the carapace; border entire, or with posterior projection or 

 indentation; margin usually present, varying in width and character; 

 compound eyes oval, situated at the antero-lateral border, much re- 

 sembling those of a trilobite; appendages nearly as in those of embry- 

 onic Limulus. 



Cyclus communis, n. sp. Plate XIV, figs. 1, la. 



• Carapace subhemispherical, circular in outline. Lateral profile 

 view a semioval, the highest point being a little back of the center 

 of the carapace. Border entire, with a narrow, nearly vertical margin, 

 which is separated from the main part of the carapace by a shallow 

 furrow. A narrow, inconspicuous median ridge extends from the 

 posterior margin to the center of the carapace. On each side of its 

 anterior half is a narrow furrow, each of which on reaching the end 

 of the ridge continues in an antero-lateral direction for a short dis- 

 tance and then again becomes parallel to the median ridge. The di- 

 verging furrows thus form a polygonal area, open anteriorly. Within 

 this area are situated three inconspicuous very slight elevations, which 

 are symmetrically disposed with reference to the median line of the 

 carapace, a single unpaired one posterior to the paired anterior ones, 

 all approximately equal in size. The surface of the carapace is 

 thickly covered with rather coarse granulations, with the exception 

 of the anterior portion, which is almost smooth. In one specimen 

 the coarse granulations and their interspaces are occupied by still 

 finer granulations. On the antero-lateral border is a prominent oval 

 or elliptical-shaped compound eye with distinct facets. 



Measurements. Eudora specimen. Kansas City specimen. 



Length 6 mm 4i mm. 



Width 6 mm ii mm. 



Height 2 J mm 2] mm. 



Width of margin I mm. 



Compound eye £ mm. X 1 nim. 



Position and locality: Upper Coal Measures, Iola limestone, Kan- 

 sas City, Mo.; Lower (larnett limestone,* Eudora, Douglas county, 

 Kansas. Many specimens. 



This species resembles in several respects C. jonesiamts H. Woodw. 

 but presents the following differences: It is a little smaller; is cir- 

 cular in outline instead of elliptical ; the anterior part of the carapace 



*For the other fossils occurring in this limestone, see paper by the author, 1. c. 



