36 



The strong development of the seventh costals, found in the Red Deer river carapace, 

 resulting in a reduction of the eighth pair of costals, is probably an irregularity of growth 

 of no specific importance. 



Fig. '2. — A, The lower or outer surface of the right hyoplastral and hypoplastral bones of Trionyx fomalun ; B, the 

 lower surface of a left hyoplastal. Natural size. 



Trionyx vagans. Cope. 

 Plate I, figs. 3 and 4. 



Trionyx vagans, Cope. 1874. Bull., U. S. Geol. Surv. Terrs., No. 2, p. 27: and 1875, Vertebrata 

 of Cretaceous Formations of the West, p. 96, pi. vi, figs. 13 and 14. 



Trionyx vagans, Lambe. 1902. Geol. Survey of Canada, Summary Report for 1901, p. 8], pis. 

 iii and iv. 



