Neurankylus eximius, Lambe, 1902

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 : 42-43

Neurankylus eximius .

Sp. nov.

The carapace of a turtle, represented by costal and other bones, shown in fig. 7 , is remarkable for certain peculiarities of structure. Of the seven costal bones obtained, from the middle and posterior parts of the carapace, four were found as shown, united to a large neural and a suprapygal bone. The other three costals, viz., the third pair and the right fourth were with the posterior costals but not in place. The fifth pair of costals was missing. The sulci indicating the junction of the costal shields seem to be normal in their position on the 4th, 6th and 8th costal bones. What is apparently a 9th costal succeeds the 8th costal bone. The 1th, 8th and 9th pairs of costals do not reach the median line of the carapace, but are separated by a large bone that is probably formed by a coalescence of the 8th neural with a suj)rapygal. This enlarged 8th neural is suturally united, for some distance with the vertebral ends of the Tth costal bones, for the whole of their breadth to the 8th costals and to a considerable portion of the supposed 9th costals. It increases in breadth posteriorly and effects a sutural union with a suprapygal whose breadth greatly exceeds its length. The rib-heads of the costals are well formed, those of the 9th costals being as fully developed as the others. No marginal bones were found with the remains of the carapace. Anterior to the point " a " on the outer edge of the 9th costal, vacuities seem to have occurred between the costals and the marginals, judging from the appearance of the outer margins of the 8th and 9th costals. From the point " a " backward a suture extended for the union of the last marginal and the pygal bone. The surface of the neural and the suprapygal is raised medially into a low, rounded, longitudinal ridge.

No very decided sculpture is shown on the surface of the bones. Striations occur adjoining and at right angles to the suttires; elsewhere there is a slight roughness in places, more particularly toward the vertebral ends of the costals, which on close examination is seen to be produced by small, obscure and irregular depressions separated by very faint ridges. Comparatively large, concentrically curved groove-like markings also occur on two of the costals.

The great development of the last neural by apparent coalescence with a suprapygal, the resulting compression of the pygal region and the addition of a 9th pair of bones to the series of costals, form a combination of characters that is both interesting and uniqiie.

A new genus is here proposed for this Mid-Cretaceous type that is thought to show gTeater affinity to the Chelydridcp. than to any other groujp.

Belly River series, Red Deer river, 1901.

Figures

Fig. 7. Part of the carapace of Neurankylus eximius, one-third the natural size. N. 3, //, &c., neural bones;, C. 3, 4> £&«, costal bones;.spy, suprapyg-al bone; r, rib-end. The heavy lines indicate tlie boundaries of the epidermal shields, the sinuous ones the sutures between the bones, and the dotted ones the parts restored.