THE PELVIC ARCH AND TAIL. 137 



The pelvic arch in Tinoceras is similar, in its general features, to that 

 of JJinoceras, but presents various differences which are apparent in 

 comparing the figures 134 and 135, above, with the corresponding views 

 of the type specimen oi' DiiKJcenis mirahile represented in Plate XLI. 



The sacrum in Dinoceras differs from that of Mastudon Americauus in 

 having four sacral vertebrae instead of five, and mucli larger transverse 

 processes, for articulation with the ilia. The foramina between these 

 processes are also proportionally much larger. Only the first two of the 

 processes unite strongly with the ilium, instead of four, as in the mastodon. 

 Both the sacrum, and the face for attachment to the ilium, are 

 proportionally much shorter than in the mastodon. 



The more important dimensions of the pelvic arch in the type 

 specimen of Dinoceras iiilnibilr, and in one individual of Tinoceras ingens, 

 are the following : 



Measurements of Pelvif:. (Dinoceras mirable. No. 1036.) 



m. 



Greatest transverse diameter, across ilia, — 1.120 



Horizontal diameter of pelvic opening (approximate), — .350 



Vertical diameter of pelvic opening (approximate), . .250 



Diameter across acetabula, - - — ---• — .660 



Diameters of acetabulum, .110-125 



Diameters of thyroid foramen, . .075-. 1 50 



Length of symphysis pubis, ._- : --■ -140 



Length of four sacral vertebra; (approximate), .245 



Extent of transverse processes of first sacral, — 330 



Horizontal diameter of anterior face of first sacral, ^110 



Vertical diameter of anterior face of first sacral, .075 



Length of first sacral centrum, 075 



Measurements of Pelvis. (Tinoceras ini/ens, No. 1497.) 



m. 



Greatest transverse diameter, across ilia, 1.180 



Horizontal diameter of pelvic opening (approximate), - . .400 



\'ertical diameter of pelvic opening (approximate), . . . .300 



Diameter across acetabula,.. .. — -700 



Diameters of thyroid foramen, - .060-150 



Length of symphysis pubis, -. -. 140 



Length of four sacral vertebra}, -. --- --95 



Extent of transverse processes of first sacral, .. -- 355 



Horizontal diameter of anterior face of first sacral, .117 



18 



