Marsh, Am. Jour. Sci. (2), XXXIV, pp. 1-16, pls. i, ii, 1862.
Agassiz, Am. Jour. Sci., XXXIII, p. 138, 1862.
Marsh, Quart. Jour. Geol. Soc., XIX, pp. 52-56.
Hay, Cat. Fossil Vertebrates (Bull. U. S. Geol. Surv. No. 179, p. 421, 1902).
Type: Specimen No. 1648, Yale University Museum.
Horizon and locality: South Joggins, Nova Scotia (Coal Measures).
The genus and species are founded on two vertebral bodies of the stereospondylous type from the Coal Measures of the South Joggins, Nova Scotia. Marsh's description ([404]) is as follows:
"The general form of the vertebræ is cylindrical, but their sides are compressed obliquely, which gives to the contour of the centra a subhexagonal appearance. They are much flattened in the direction of the antero-posterior diameter, which has to the transverse diameter the proportion of 1 to 3. Both the articular terminal facets are deeply and equally concave; but from the center to the margin the surfaces are convex, and this convexity is greatest near the center. * * * The cavities for the reception of the intervertebral matter begin immediately from the margin, and are considerably deeper than the corresponding parts of the Ichthyosaurus, indicating a greater degree of flexibility in the vertebral column. The margins of the vertebra; are somewhat raised, as if they had yielded to a forcible compression applied longitudinally; and hence the lateral surfaces of the centers are concave in an antero-posterior direction. This concavity is greater in the upper half of the vertebra and was undoubtedly more marked originally than at present, since the appearance of the margins indicates considerable abrasion. The non-articular surfaces of the centra are smooth and regular; and the external fibres of the osseous tissue are singularly reticulated.
