MERRIAM: TRIASSIC ICI1TII VOSACKMA. 147 



their height being considerably less than the height of the centra. The distal 

 ends of the neural spines are much expanded and thickened, and the upper por- 

 tion is slightly domed, instead of excavated as in />'. (illispinus. A horizontal 

 cross-section of the upper portion of the neural spine is nearly circular, and at 

 the upper end of the spine the transverse diameter is considerably greater than 

 the corresponding diameter immediately above the /yga pophyses. The xygapo- 

 physial facets are well developed although not very large. 



MEASUREMENTS OK VERTEBRAE. SPECIMEN 9614. 



Height of centrum of vertebra from middle dorsal region 118 mm. 



Transverse diameter of centrum .... alia 



Anteroposterior diameter of centrum 34 



Length of upper arch 79 



Transverse diameter of neural spine behind anterior zyga pophyses 25 



Transverse diameter of neural spine at upper end 35 



a Approximate. 



Well preserved ribs (pi. 18, fig. 6) are present with each of the vertebral 

 centra with this specimen. The form of these ribs is in general similar to that 

 of the ribs in S. o*inonti, excepting that the shaft and head are apparently 

 somewhat heavier. The posterior side of the shaft is strongly grooved in the 

 proximal half. The distal portion has been broken away in all cases. As in 

 S. osmonti and S. aUispinus, the upper portion of the articular face of the 

 rib is turned rather sharply outward from the plane of the lower portion of 

 the face. 



Of the known species this form is evidently nearest to S. careyi and S. alti- 

 */H'IIHH. Though the vertebrae cannot be compared closely with the known type 

 of S. careyi, owing to their not belonging in the same region of the column, 

 they seem to be somewhat thinner anteroposteriorly. Their fore-and-aft diam- 

 eter equals about 29 per cent, of the height of the centrum while in S. careyi it 

 equals about 37 per cent. 



In S. aUispinus vertebral centra from a region of the column corresponding 

 closely to that represented in specimen 9614 are much thicker than in this 

 specimen. Also, the neural arches are relatively almost twice as long, and 

 are much less expanded distally. 



Considering that specimen 9614 represents a different part of the vertebral 

 column from that seen in the type of S. cairi/i, it is not improbable that it rep- 

 resents the same specific type or at least a closely allied species. The extremely 

 specialized character of the anterior limb found here one would expect to find 

 in S. careyi of all the known species, as it is the latest and the largest of the 

 several types. 



