35 



Small, shallow, rovinded depressions mark the surface of the neiirals and the inner 

 ends of the costals. In the latter, as the distance from the neurals increases, the de- 

 pressions gradually grow larger and more decided, becoming often reniform or oval, and 

 frequently coalescing, until in the distal ends of the costals a few more or less conti- 

 nuous furrows are formed parallel to the outer margins of the plates. These furrows are 

 a conspicuous featiire in the sculpture ; they are not so well marked on the posterior 

 margin of the carapace, but are well developed near the front edges of the first costals. 

 In the neurals and inner halves of the costals there is a narrow, smooth strip, devoid oi 

 sculpttire, bordering the sutures. The rib-heads are well developed. 



Measurements. 



M. 



Estimated length of carapace along median, line (6 -j% inches) . . . . , • 168 



Length of carapace, along median line, from anterior edge of neural 1 to 



posterior margin -ISS 



Maximum breadth of carapace (8 j^ inches) '214: 



Length of first neural (1 + la) -033 



Length of second neural , . '023 



Maximum breadth of second neural ■ 017 



Thickness of fourth costal at centre near inner end • 005 



Thickness of fourth cosial at centre near outer end ■ 005 



Thickness of eighth costal at centre • 005 



The hyosternal and hyposternal bones of this species, shown in fig. 2, page 36, 

 belong to individuals of larger size than the one represented by the carapace. The mis- 

 sing parts in fig. 2 are restored from a number of other specimens in the collection, of 

 which no two are exactly alike. The sculpture differs considerably from that of the 

 carapace and is shown on plate I, fig. 2. 



Belly River series. Red Deer river, 1901 ; also numerous costal bones and fragments 

 of the carapace with separate neural bones as well as hyoplastra and hypoplastra and 

 bones of the endoskeleton, 189*7, 1898 and 1901. 



Dr. Gr. M. Dawson collected fragments of the carapace on Belly River, N. W. T. 

 (Nos. 40 and 41) in 1881. 



Trionyx planus,* Owen and Bell, a British Lower Eocene species, described from the 

 posterior half of the carapace, bears a strong general resemblance to T.foveatus as regards 

 the sculpture, and also in the absence of the seventh and eighth neurals, accompanied by 

 a similar ctirtailment of the sixth neural. 



■ Monograph of the British Reptilia of the London Clay, part I, p. 5S, tab. XIX c, 1S4&. PaliBontographical Society. 



