Logan.] The Invertebrates, Niobrara Group. 501 



narrow, rounded, slightly convex, the surface marked by par- 

 allel stria?; height, four mm.; breadth, two mm. Terga tri- 

 angular, with the base rounded ; slightly convex, the surface 

 smooth ; length, eight mm. ; maximum breadth, four mm. 

 Scuta large, convex, quadrangular, its superior lateral border 

 somewhat rounded ; rostral border straight, surface marked ; 

 length, eight mm. ; maximum breadth, five mm. Carino-lat- 

 erals long, triangular in outline, the surface marked by trans- 

 verse lines ; length, eight mm. ; breadth, three mm. Superior 

 laterals shorter, resembling the carino-laterals in general shape. 

 Peduncle short ; its maximum breadth, six mm. ; composed of 

 seven rows of plates ; plates quadrangular, with the upper bor- 

 der curved ; six or seven larger plates in the upper part of a 

 row, succeeded below by about ten very much smaller ones. 

 Type specimen adhering to the shell of an Inoceramus by its en- 

 tire length. 



The type specimen was presented by Mr. M. R. Watson, of 

 Trego county, and had evidently come from the lowermost beds 

 of the Upper Niobrara, probably from the Hesperornis beds. 



