GILMORE: OSTEOLOGY OF BAPTANODON (MARSH) 101 
be supplemented somewhat by the more complete vertebral series in the collections 
of the University of Wyoming. 
With skeleton No. 603 there are thirty or more vertebre in various degrees of 
preservation, but there are none arranged serially. However, every part of the 
column is represented. 
Specimen No. 878 has a series of twenty-one vertebree extending from the atlas 
backward. (See Pl. VII.) The first fifteen are in a fair state of preservation but the 
remaining six are very imperfect. The spinous processes are only preserved in a few 
instances. 
No. 919 which is a much larger individual has a series of ten cervicals com- 
mencing with the atlas, a second series of eleven from the anterior dorsal region 
posterior to the point where the diapophyses become distinct from the neurapo- 
physial articular surface; a third section of eleven posterior dorsals commencing 
just posterior to the first vertebra having the diapophysis and parapophysis united 
to form a single node-like articulation. The fourth and last section contains parts 
of twelve anterior caudals, these show the rapid decrease in the size of the centra 
posteriorly as previously pointed out by Knight.” 
The centra in all regions anterior to the extreme caudals are deeply biconcave. 
These concave surfaces, with the exception of the anterior face of the atlas, begin 
close to the periphery and slope in rapidly but evenly to the center. In this 
respect Baptanodon may be distinguished from O. icenicus, as Lydekker * observes 
of the vertebree referred to the latter genus. ‘The cervical region with the cupping 
of the anterior face of the centrum confined to the central portion, and surrounded 
by a flattened periphery.” There are some isolated centra of this character in the 
collections of the Yale Museum, labelled as coming from the Baptanodon Beds of 
the Rocky Mountains. From this slight evidence it would appear as though the 
genus Ophthalmosawrus may also occur in this country. 
The upper arches in this genus as in all previously described Ichthyosaurians 
are free from the centra and were united to them by synchondrosis. The centra 
are always short antero-posteriorly as compared with their breadth and height. 
Atlas and axis (at. and ax.).— In Baptanodon as in nearly all adult members of 
the Ichthyosauria, the centra of the atlas and axis are completely fused, so much so 
that one would hardly suspect the existence of two vertebree if it were not for the 
presence of the two sets of arches upon their dorsal surfaces (see figs. 10 and 26). 
These vertebrae are represented in all three specimens, Nos. 603, 878 and 919. Those 
35 Knight, W. C., ‘‘Some Notes on the Genus Baptanodon, with a Description of a New Species,’? Am. Jour. of 
Sei. (4), Vol. XV., 1903. 
36 Lydekker, lit. cit. 
