66 The Ottawa Naturalist. [June 



Length along- median line from anterior end to posterior 



border of pectoral shield 295 



Breadth from median line to lateral suture ( = half of breadth 



of plastron) 280 



Length of entoplastral 085 



Maximum breadth of entoplastral 123 



Thickness midway between gulars 035 



Thickness at centre of gular shields 033 



Thickness on median line at posterior border of pectoral 



shield 013 



Thickness at posterior edge of hyoplastral near left bound- 

 ary of abdominal shield 007 



Thickness in axillary region near lateral suture 032 



Thickness midway between entoplastral and the axillary 



notch . . .025 



In 1882 Dr. J. F. Whiteaves had labelled the two marginal 

 bones from the Red Deer River with the name Compscmys 

 variolosus, and to him belongs the credit of having first noticed 

 the occurrence of this species in Canada. 



The writer is indebted to Dr. O P. Hay, of the American 



Museum of Natural History, New York, who since the above was 



written, has compared some of the Red Deer River material, sent 



to him, with the type of Cornpsemys variolosus, Cope, and confirms 



the correctness of the writer's specific identification. Dr. Hay 



informs the writer that in the type there is little, if any, of the 



carapace represented and that the anterior lobe of the plastron is 



missing. Also that the specimen shows the central portions of ■ 



the plastron, and the posterior lobe, which latter is broadly 



rounded. 



EXPLANATION OF PLATES. 



Plate in. 



Figure 1- -The pla^stron of ^Idoats variolusiis (Copo); from the Cretaceous 

 of Alberta. One-sixth natural size. I G, Interjjular shield ; G, Gular do.; 

 HUM, Humeral do.; PEC, Pectoral do.; AB, Abdominal do.; FEM, 

 Femoral do.; AN, Anal do.; EP, Epiplastral bone ; ENTP, Entoplas- 

 tral do.; HYP, Hyoplastral do.; HPP, Hypoplastral do.; XP, Xiphi- 

 plastral do. 



Figure 2 — The upper or inner side of the plastron o( -Idociis vinrio/ostts (Cope). 

 One-sixth natural size. P, surface for the articulation of the pubis. 



