Adocus variolosus, Cope, 1876

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 : 39-42

Adocus variolosus , Cope, (sp.)

Plate II, figs. 1, 2 and 3 .

Compsemys ogmius , Cope. 1875. Report on the Geology and Resources of the forty-ninth parallel, appendix B.

Compsemys variolosus , Cope. 1876. Proc. Acad. Nat. Sci. Philadel,, vol ..xxviii, p. 2.57.

Adocus variolosus , Lambe. 1901. Ottawa Naturalist, vol ..xv, p. 63, pis. iii, iv, v, and vi.

The proportions of the component feloments of the plastron of this species can be seen by referring to figures 4 and 5 , where restored outlines are given, based on two fragments of the same shell, which are represented in the figure by the shaded portions. The sutures between the bones are shown by the sinuous lines and the boundaries of the shields by the heavy ones. The dotted lines represent the supposed shape of the end of the posterior lobe, the direction of the sulcus defining the front limit of the femoral shields, and the position of the sulcus that probably crossed the xiphiplastrals, whilst the extent of the hypoplastrals is conjectural.

IG, Intergular shield; G, Gular do. JIUM, Humeral do. PEC, Pectoral do. AJJ, Abdominal FEM, Femoral;;; do.; do. AX, Anal do.: EP, Epiplastral hone; SNTP, Entoplastral do.; HYP, Hyoplastral do. HPP, Hypoplastral do. XP, Xiphiplastral do.

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The plastron is flat except at the sides where it beuds evenly upward, the lobes are short and broad, and the sternal bridge long. The entoplastral is roughly pentagonal and rather broad. The epiplastrals are of not unnsual size and shape, whilst the hyoplastrals are relatively large. A divided intergular shield separates two small gulars, behind which are well developed humeral shields. The pectorals narrow rapidly toward the sides where they and the abdominals meet a series of inframarginals that overlap the peripheral bones. All the sulci are deep and conspicuous except those marking the position of the inframarginals, the anterior boundaries of the gulars, and the division of the intergular. These latter, however,, are sharply and clearly defined. The sutural line between the hypoplastrals and the xiphiplastrals is shown in the smaller of the two fragments.

The sculpture consists, when most rugose, of well excavated pits of a rounded hex- agonal outline arranged quincuucially; the dividing ridges are angular and narrower than the pits are wide, their angularity and height being more pronounced at the junction of every three pits with each other. The formation thus, of three-surfaced, pyrami- dal projections between the excavations, gives to the shell of this turtle its very characteristic and rugose appearance. There are about seven pits in a space of 20 mm. In places a number of pits, as many as half a dozen or more, may coalesce so as to form a continuous groove. The sculpture is most rugose near the edges of both carapace and plastron, elsewhere its roughness is modified and generally toward the centre of the shell the surface is comparatively smooth.

On the inner or upper side of the plastron (fig. 5, page 39) the rugose sculpture extends inward for some distance from the free edges of the lobes, more particularly at the extreme anterior end, where also the bone is very much thickened. A decided thickening also occurs in the axillary region. The oval outlines on the xiphiplastrals (P, fig. 5 ) show the position of smooth, slightly raised, flat surfaces that are apparently facets for the articulation of the pubic bones.

Large fragments of the carapace show that the cosials are thin and are united to the comparatively thick marginal bones by suture and that the sulci are deep and well defined. In some of the marginal bones the rib-prolongations from the adjacent costals are preserved. The rib-heads of the costals are apparently well developed.

In 1901, the anterior half of a plastron ( fig. 6 , page 41), with the front border of the carapace intact, was obtained below the mouth of Berry creek. This specimen, representing an individual, with a plastron about "840 mm. in length, gives the relative position of the plastron to the carapace anteriorly and also shows an enlargement of the right pectoral shield to the left of the median line of the plastron resulting in a decided diminution in the size of the left pectoral shield.

Additional material includes two or three neural bones, some of the bones of the endoskeleton and a few small, thick, conical scutes from the tail. These latter have an upper surface whose sculpture is an exaggeration of that of the most rugose parts of the shell.

The types of Compsevxyx og-mius, Cope, from the '' Fort Union group" of Milk river, consisting of two small, poorly preserved fragments of costal bones, show sculpture markings so similar to those characteristic of A. variolosus, that the writer is of the opinion that the two species are identical. On account of the poorness of the type specimens of C. ogmius and to avoid confiision the specific name variolosus is retained.

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The foregoing characters indicate a Chelonian that cannot be retained in the genus Compsemys , which is closely allied to Pleurosternon and possesses a mesoplastral element. The presence of two small gular shields separated by a divided* or double intergular shield (in reality two intergulars), and of a series ot inframarginals, the absence of a mesoplastral and of a sutural union of the pelvis with the plastron, together with an abbreviation of the lobes and a decided lengthening of the sternal bridge are characters that suggest such close affinities to the genus Adocus of Cope, that this species has been referred to that genus.

Measurements.
	M.
Estimated length of plastron (281 inches)	720
Length along median line from anterior end to posterior border of pectoral
shield	-295
Breadth from median line to lateral suture (= half of breadth of plastron).,	"280
Length of entoplastral	085
Maximum breadth of entoplastral	- 123
Thickness midway between gulars	035
Thickness at centre of gular shields	-033
Thickness on median line at posterior border of pectoral shield	'013
Thickness at posterior edge of hyoplastral near left boundary of abdominal shield	007
Thickness in axillary region near lateral suture	'032
Thickness mid way between entoplastral and the axillary notch.	025

Dr. O. P. Hay has informed the writer that in the type specimen there is little, if any, of the carapace represented, that the anterior lobe of the plastron is missing, and that the specimen shows the central portions of the plastron, and the posterior lobe, which latter is broadly rounded.

Belly Eiver series, Eed Deer river, 1 89*7, 1898 and 1901.

Fragments of the shell had been collected as follows: Professor John Macoun, Mackay creek, 1880 (Belly Eiver series); Dr. Gr. M. Dawson, on Old Man river, below Fort McLeod, 1881 (Willow creek subdivision of the Laramie); Mr. E. G-. McOonnell, Eed Deer river, 1882 (Belly Eiver series).

Figures

PLATE II. Adocus variolosus, Cope. (sp.) Fig. 1. Plastron, lower or outer surface 0f specimens represented in figures 4 and 5, page 39,' one-third natural size. Page 39. Fig. 2. The same, upper or inner surface. Fig. 3. The lower surface at the anterior end of the same plastron, natural size to show the character of the sculpture.

Fig. 4 Plastron of Adocus variolosus one-sixth the natural size. ;

Fig. 5 Uppper or inner surface of the same plastron, from Red Deer river, Alberta.

Fig. 6. Anterior half of the shell of Adocus variolosun, from Red Deer river; ventral aspect showing the front margin of the carapace, One-fifth natural size