Trionyx vagans, Cope, 1874

Lambe L. M., 1902, New genera and species from the Belly River Series (mid-Cretaceous), Geological Survey of Canada Contributions to Canadian Palaeontology 3, pp. 25-81 : 36-38

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.

This species was first described from " a ntimber of fragments of costal boues and perhaps of sternals also from the " Lignite Cretaceous of Colorado; near the mouth of the Big Horn river, Montana; Long lake, Nebraska; found at the last two localities by Dr. Hayden." Later, in 18 Y 5,in "TheVertebrata 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.

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. broadest at the sides of the carapace aud narrowest in front, extends along the whole of the peripheral edge.

As regards a divided first neural in species of this genus, it is interesting to note that Lydekker, in describing T. melttensis, from the Miocene of Malta, in 1891 ^Quarterly- Journal of the G-eological Society, voL xlvii, p. 37, iig. 1), mentions the occurrence in the Miocene species of a divided first neural, and remarks 37) that " all the fossil species (p. hitherto described, of which the entire carapace is known, agree with the normal type in having but a single long neural between the first pair of costals."

Measurements.
	M.
Length of carapace along median line (18 1/2 inches)	470
Maximum breadth of carapace (' 2/10 inches).	590
Breadth of first costal at inner end	'075
Thickness of same near inner end	009
Thickness of same at outer end,	'012
Breadth of fifth costal at outer end	"119
Thickness of same at outer end	"013
Breadth at mid-length of seventh costal	-036
Thickness at centre of eighth costal	'010
Maximum breadth of neural 1	056
Maximum breadth of neural la	039
Length of same	043
Thickness of nuchal plate at left end	'018
Length of vertebral centrum	045

Belly River series, Eed Deer River, 1897, 1898 and 1901; besides the carapace above described, separate costals and neurals, and parts of the endoskeleton.

Also in 1880, Professor John Macoun, neurals and fragments of coatals, from Mackay creek, near Walsh, a station on the C. P. R., about twenty-eight miles east of Medicine Hat; aud in 1881, Dr. G-. M. Duwsou, from Belly river, N. W.T. (No. 41), fragments of costal bones.

Figures

PLATE I. Fig. 1. Trionyx foveatus, Leidy, upper surface of the carapace shown in figure l, p. 34, * one-half the “ nhn-n] cian puma 22 JÃIUUUICUI Dllıbı J. luau LII-Ia Fig. 2. Trionyx ƒoveatus, lower or outer surface of a right hypoplastral bone; natural size. Page 35, Fig. 3. Trionyx vagans, Cope, upper surface of carapace shown on page 37, figure 3,' slightly less than one-fourth natural size. Page 36. Fig. 4. Portion of the upper surface of thc same carapace, natural size; to show the sculpture.

FIG. 13. -Stereocephalus tutus. Dermal plate from Red Deer river one - sixth the natural size. A, side view; B, view from above. Provisionally associated with S. tutus.)

Fig. 3. Carapace of Trionyx vagansi, 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.