MEKKIAM: TKIASSIC ICHTHYOSAURIA. 127 



cavated. There is a single rib articulation which extends from the base of the 

 ii])])or arch to a point a little below the middle of the centrum, but the lower 

 end does not swing forward to the anterior margin, as is generally the case in 

 ('. ix'frinus. This form can be only tentatively separated from G. petrinus, 

 but with the differences shown in the small amount of material available it is 

 not considered advisable to refer it to that species, and it may be referred to 



MKASI-KK.MKNTS. NO. KKil'O. 



Posterior dorsal rib. 



Vertical diameter of rib bead ............................................................. 60 linn. 



Anteroposterior diameter of rib head ... 36 



Caudal rib? 



Length .................................................................................................................... 130 



Greatest diameter of middle of shaft ......................................................................... 21 



Greatest diameter of less compressed end .............................................................. 48 



Thickness of the less compressed end ........................................................................... 35 



Greatest diameter of more compressed end ........................................................ 53 



Thickness of the more compressed end ................................................................ :.... 25 



Preaxial epipodial of posterior limb (?). 



Axial diameter .................................................................................................................................... 123 



Transverse diameter of proximal end ........................................................................... 140 



Transverse diameter of median region ........................................................................ 114 



Transverse diameter of distal end .................................................................................... 146.5 



Greatest thickness of proximal end ............................................................................. 65 



Postaxial epipodial of posterior limb ( ?). 



Axial diameter .................................................................................................................................... 135 



Transverse diameter of proximal end ........................................................................... 95 



Transverse diameter of median region ........................................................................ 77 



Transverse diameter of distal end ................................................................................. 180 



Greatest thickness at proximal end ................................................................................. 50 



MEASUREMENTS OF ANTERIOR DORSAL VERTEBRA, NO. 10821. 



Height of centrum ....................................................................................................................................... 110 mm. 



Transverse diameter of centrum ....................................................................................... ........... 110 



Anteroposterior diameter of centrum ....................................................................................... 64 



TORETOCNEMUS Merriam. 

 Toretocnemus Merriam, Univ. Calif. Publ. Geol., vol. 3, p. 251, pi. 24. 



Vertebral centra relatively elongated. Neural arches not greatly thickened, 

 but showing distinct lateral ridges. Candal vertebrae with long Y-shaped 

 lower arches. Middle dorsal rib heads sharply divided into lower head and 

 tubercle. Diapophyses and parapophyses of vertebral centra widely separated 

 in the middle dorsal region. Posterior limbs equaling the anterior in size. 



