Trionyx foveatus, Leidy., 1860

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 : 33-36

Trionyx foveatus, Leidy.

Plate I, figs. 1 and 2 .

Trionyx foveatus , Leidy. 1860. Trans. Amer. Philos. Soc. vol. xi, 148, pl. xi, figs. 1 and 2.

p. " " Lambe. 1902. Geol. Survey of Canada, Summary Report for 1901, p. 81, pls. I and II.

Trionyx foveatus was originally described by Leidy from small fragments of costal and sternal bones from the Judith River beds of Nebraska.

A carapace, from the Belly River series of the Red Deer river district, lacks only the nuchal plate, which unfortunately was missing.

This carapace ( fig. 1 ) is a little broader thau long, and is only slightly conA-ex. Seen from above, its anterior, posterior and lateral curves are flattened so as to make the outline subquadrangular. The eight pairs of costals are entire and there are six neural bones of which the anterior one is divided. Neural 1 is broader than long with convex sides, neural la is longer than broad, broadest near its posterior end and has concave sides. Neurals 2, 3 and 4 are six-sided, neural.5 is oblong, and neural 6, lying for the most part between the sixth costals, is shield-shaped, narrowing to a point behind. The seventh costals are suturally united at their inner ends, where they develop a breadth sufficient to separate the eighth costals from each other. These last are subtriangular in shape, with three convex sides. The nuchal plate was evidently small, as the lateral termination of the suture (c, in figure 1 ) between it and the first costal indicates a side extension not far past a point in advance of the mid-length of the first costal its lateral ends lie beneath the front border of the first costals and are not seen from above.

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 depressions 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 continuous 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 6/10 inches)....,	168
Length of carapace, along median line, from anterior edge of neural 1 to posterior margin	-163
Maximum breadth of carapace (8 4/10 inches)	'214:
Length of first neural (1 + 1a)	-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 missing 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.

.

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.

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. 1. Carapace of Trionyx Jovealiis, from Red Deer river; a, outline of the transverse curve of its upper surface. Five-eighths the natural size. NIX, Nuchal hone (restored); Nl, la, 2, &c., Neural bones; Cl. 2. &c., Costal bones.

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