120 G. R. Wieland — Upper Cretaceous Turtles. 



to the prior one, Euclastes* For reasons given below, the 

 species is considered a new one, and I take great pleasure in 

 naming it in honor of Mr. Hugh Gibb, Preparateur at this 



Museum for more than twenty years 

 past, and an excellent naturalist. 



Description. — The general out- 

 line of the Carapace is broadly sub- 

 elliptical, the nuchal having only, 

 slight recurvature, and the pygal 

 region forming a very obtuse angle. 

 As may be seen by referring to the 

 side view, figure 3, the body is rather 

 flat. The general outline is not un- 

 like that of Kacliuga lineata, the 

 plastron being, however, much flat- 

 ter and quite different. To get any 

 comparison of plastral form, it is 

 necessary to turn to the Dermatemyd- 

 idse or to Chelydra. The very large 

 posterior marginals rise at a rather 

 low angle. The surface of the bony 

 plates is seldom pitted, except by 

 accident, and is, especially over a 

 large portion of the pleuralia, marked 

 by closely set fine lines. 



(A) Carapace. — Composed of 51 

 bony plates, with the boundaries of 

 the 38 horn shields all clearly marked 

 as deep and distinct furrows. 



(1) Bony Plates: Marginals 11 

 pairs, all united to pleurals by su- 

 tures ; the 2d deeply round pitted 

 posteriorly for reception of outer an- 

 terior limb of me hyoplastron ; the 

 7th-llth of broadly oblong shape, 

 slightly concave on upper surface, the 

 inferior faces being more strongly 

 convex ; external borders forming a 

 continuous outer curvature from the 

 nuchal to the ninth, but borders of 

 Figure d.—Osteopygis GibM 9-11 and the pygal marginal slightly 

 (type). Sketch of tlie lateral convex • 4th-6th very slightly escal- 

 view of the carapace and plas- -, , ' . lim ;p r hnrdpr and 



tron as mounted, x £. iopea on inner upper ^ ooraer ana 



exposing rib tips a little ; 7th- 

 10th with . deep Y-shaped notch in inner upper border dis- 

 tinctly exposing the tips of the ribs ; rib pits flattened : mar- 



* Extinct Batrachia, Eeptilia, and Aves of North America, Trans. Amer. 

 Phil. Soc, vol. xiv, 1869, page 140. 



