37 



This species was first described 

 from " a ntimber of fragments of costal 

 boues and perhaps of sternals also " 

 from the " Lignite Cretaceous of Colo- 

 rado ; near the mouth of the Big Horn 

 river, Montana ; Long lake, Nebraska ; 

 found at the last two localities by Dr. 

 Hayden." Later, in 18Y5,in "TheVerte- 

 brata of the Cretaceous Formations of 

 the West" thesamedescription appears; 

 this time with figures of two fragments 

 of costal bones. 



A carapace (fig. 3) referable to this 

 species, was obtained in 1901, from the 

 Belly River series of Red Deer river 

 below Berry creek. 



3. — Carapace of Trionyx vagan>i, from Red Deer ; a, out 

 line of the traverse curve of its upper surface. One-eighth the 

 natural size. Letters as in figure 1, page 34. 



It is broader than long, the breadth 

 exceeding the length by more than one- 

 sixth, and is only moderately convex. In outline, as seen from above, it is flat behind with 

 the sides curving broadly to the front margin, at the centre of which there is a shallow 

 concavity. The shell protrudes where the ribs pass outward from beneath, causing the 

 lateral margin to be sinuous, the sinuosity being most marked toward the front in the 

 first, second and third pairs of costal plates. Of the eight pairs of costals, the first costals 

 are the broadest at the inner ends, whilst the fifth are the broadest distally. The seventh 

 costals are extremely narrow throughout their length and the eighth pair is w^ell developed. 

 The first costals increase in breadth rather suddenly at their outer ends and are separated 

 by a divided first neural plate. The neurals gradually decrease in breadth to the fifth^ 

 their sides being not so nearly parallel to each other as those of the corresponding plates 

 in T.foveatus. The sixth and last neural is very much reduced in size and is irregularly 

 oval m outline. Of the protruding rib-ends, all the six of the left side were secured, in 

 a fair state of preservation, except the one belonging to the first costal and it was obtained 

 in part. The rib-heads are well developed. In the figure, the nuchal plate is represented 

 as entire. Of the carapace under consideration, the central part only of the nuchal plate, 

 extending from the margin in front to the suture behind, was found, but fortunately the 

 left end of a nuchal, of another individual of similar size, showing the left front margin 

 and the suture between the plate and the first costal with part of the latter adherent, 

 supplied the deficiency. The sculpture consists of a network of narrow ridges, ramifying 

 and inosculating so as to enclose small, sunken areae of irregular shape and size, the arese 

 being generally wider than the ridges are broad. The frequent confluence of a varying 

 number of arete results in a more open pattern, the ridges at times showing a tendency to 

 run in parallel lines. The sculpture is not so distinctly defined near the sides of the carapace 

 as it is toward and at the centre and anteriorly, but in the hinder part it is more decidedly 

 rugose, the ridges being here higher and the enclosed areae larger. Near the intercostal 

 .sutures, more particularly in the inner halves of the costal bones, the scrrlpture is partially 

 effaced and consists of low, poorly defined parallel ridges at right angles to the sutures, 

 forming a distinct border, with a maximum breadth of about 5 mm. A smooth border. 



