DORSAL VERTEBKJE OF HESPERORXIS. 51 



extends somewhat below. The diapophyses in this vertebra begin to 

 shorten, though but slightly, and are directed horizontally outward, and 

 somewhat anteriorly. Neither in front of, nor behind their base, is there 

 any proper pit in the vertebra. The neural spine is somewhat higher, but 

 of less antero-posterior extent, than in the preceding vertebra, and the 

 surfaces before and behind near the base are rather more roughened for 

 the attachment of lig'aments. 



To indicate the range of variation in the vertebrae of Hesperomis 

 regal is, measurements of the twenty-first vertebra in five individuals are 

 given in the tables below. Number 1200 is the type of the species. 



Measurements of Twenty-first Vertebra. (No. 1200.) 



Length of centrum, _•. 24.0 mm 



Least transverse diameter of centrum, 9.0 



Transverse diameters of anterior articulation of centrum, 16.5-23.0 



Vertical diameters of anterior articulation of centrum, 9.0-13.0 



Transverse diameters of posterior articulation of centrum, 14.8-22.0 



Vertical diameters of posterior articulation of centrum, 10.5-18.5 



Transverse diameter of vertebra, across pre-zygapophyses, 20.0 



Transverse diameter of vertebra, across parapophyses, 27.0 



Diameters of pre-zygapophyses, 9.5-8.5 



Length of floor of neural canal, 25.5 



Length of roof of neural canal, 23.0 



Transverse diameter of neural canal, at anterior opening, 7.0 



Vertical diameter of neural canal, at anterior opening, 5.0 



Transverse diameter of neural canal, at posterior opening, ,. 8.0 



Vertical diameter of neural canal, at posterior opening, 6.0 



Diameters of articulation for head of rib, 7.0- 8.0 



Measurements. (No. 1206.) 



Transverse diameters of anterior articulation of centrum, 16.0-24.0 mm 



Vertical diameters of anterior articulation of centrum, - 12.0-13.0 



Transverse diameter of vertebra, across pre-zygapophyses, 20.0 



Transverse diameter of vertebra, across parapophyses, 25.0 



Diameters of anterior zygapophyses, 9.5-11.0 



Transverse diameter of neural canal, at anterior opening, 7.5 



Vertical diameter of neural canal, at anterior opening, 6.0 



Diameters of articulation for head of rib, 6.0- 9.0 



Length of hypapophysis, 14.0 



Height of neural spine above floor of neural canal, 33.0 



Antero-posterior diameters of neural spine, — 17.0-21.0 



