230 Illinois State Lahoratonj of Natural History. 



Shell moderately convex above, the slope uniform in front, 

 somewhat explanate above the insertion of the posterior legs, a 

 trifle depressed centrally. Third, fourth, and fifth dorsal plates 

 with an obscure rounded median ridge. Costal plates and the 

 first and fifth dorsals strongly longitudinally rugose; the three 

 central dorsals only faintly so. Nuchal plate slender, tapering 

 forward; the two adjacent marginals with outer angles pro- 

 jecting. Posterior five marginal plates of each side without 

 outer angles, each with a marginal notch. Plastron a little 

 rounded in front, nearly truncate; outer angles of the gulars 

 bluntly tuberculate, the anterior edges roughened. Plastron 

 broadly excised behind; anal plates with no angles. Head of 

 medium size; jaws rather strong, the upper with a very slight 

 median notch. Tympanum evident. Feet strong, the posterior 

 pair greatly expanded and strongly webbed. 



Length of carapace, 9.25; width of same, 6.75; depth of 

 shell, 3.50. 



Carapace greenish olive and black above, the former 

 slightly predominating, the black confined chiefly to the mar- 

 gins excepting on the two median costals, where it forms a 

 transverse median band, the olive forming on most of the dor- 

 sal and marginal plates large quadrate central spots; marginals 

 beneath more extensively black, and with the greenish olive 

 replaced with pale yellow. Plastron pale yellow and black, 

 the latter extending along the sutures on the anterior two 

 thirds of the plastron, but occupying most of the plates of the 

 posterior lobe, leaving only central spots and part of the 

 margins yellow. Head dusky, obscurely and finely mottled and 

 spotted above with olive-brown, beneath narrowly and obscurely 

 striped with greenish. Jaws horn-color with dots and dashes 

 of black. Feet and tail dusky, with indefinite markings. 



Described from a single example taken on Long Island, in 

 the Mississippi River at Quincy. The proportions of the black 

 and yellow of the plastron are subject to considerable variation, 

 sometimes one, sometimes the other predominating. 



This is one of our rarest species. The only examples in 

 the State Laboratory collection were collected at Quincy. Mr. 

 R. Ridgway of the United States National Museum has ob- 



