from the Coal Measures of Nova Scotia. 209 



The general form of the vertebrae is cylindrical, but their sides, 

 are somewhat compressed obliquely, which gives to the contour 

 of the center a sub-hexagonal appearance. They are much flatten- 

 ed in the direction of the antero-posterior diameter, which has to 

 the transverse diameter about 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 in the corresponding arts of the' 

 /cA^^yosawrws, indicating a greater degree of flexibility in the spinal 

 column. The margins of the vertebrae are somewhat raised, as if they 

 had yielded to a forcible compression applied longtiudinally 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. 



-The neurapophyses are not anchylosedto the centrum, as in the 

 mammalia, nor connected to it by sutures, as in the crocodiles ; 

 but their union with the vertebra is indicated by two pits, which 

 served for their articulating surfaces. These depressions are sit- 

 uated on the supei-ior surfaces of the centrum, intermediate be- 

 tween the anterior and posterior margins of the extremities. They 

 are circular in form, and sink directly into the body of the verte- 

 bra; instead of being elongated longitudinally, and raised on 

 ridges, as in the Ichthyosauri. The pits are about a line in depth, 

 and in the more perfect of the fossils are not in their original 

 position ; as a fracture in the upper part of the centrum has push- 

 ed them obliquely apart, so that a line passing through their cen- 

 ters would form an angle of about 30*^ with the transverse 

 diameter of the vertebra. The depressions occupy about one-third 

 of the distance between the margins of the articular extremities, 

 indicating that the base of the neural arch was of less antero-pos- 

 terior extent than the centrum. The floor of the spinal canal is 

 narrow, being but five lines in breadth ; and its surface in the pos- 

 terior vertebra is broken by the fracture previously mentioned, 

 which passes lengthwise through its center. No neurapophyses 

 were found with these fossils, but the nature of the superior arch 



Can. Nat. 14 Vol. VII. 



