126 MEMOIRS OF THE CARNEGIE MUSEUM 
RELATIONSHIP AND CLASSIFICATION. 
In the general outlines of its structure, Bbaptanodon appears very similar to the 
European genus Ophthalmosawrus, although the true relationship of the two genera 
has long been an enigma to scientists. 
In 1888 Lydekker® considered Baptanodon a synonym of Ophthalmosawrus after 
Baur’s™ suggestion, that : ‘“ Ophthalmosaurus, Seeley. Vielleicht nicht verschieden 
von Baptanodon,” a view which he abandons later in the Catalogue of Fossil Rep- 
tilia and Amphibia in the British Museum. 
In 1898 Woodward in his Vertebrate Paleontology, p. 183, observes: ‘‘ Baptano- 
don from the Jurassic of Wyoming is remarkably similar to the European fossil and 
perhaps generically identical.” 
A number of equally eminent American paleontologists have verbally expressed 
themselves as believing the two genera synonymous. 
The presence of firmly united clavicles without suture, and the uniform bicon- 
cave cupping of the anterior cervicals, together with the development of a sixth 
digit in Baptanodon are characters which appear to be of sufficient value to warrant 
the distinct separation of the two genera. 
In the reduced size and loose attachment of the teeth, the arrangement of the 
bones of the anterior extremities, and the retention of the disk-like elements of the 
paddles in persistent cartilage, these two forms are very similar. 
The characters enumerated above indicate a high degree of aquatic specialization 
and Baptanodon, I believe, should be considered the most specialized of the known 
Ichthyopterygia. ‘The closestaffinities of Baptanodon are with Ophthalmosaurus, next 
approached by Ichthyosawrus. In some respects Baptanodon is but little more modi- 
fied to purely aquatic conditions than is found in the earlier genus Shastasawrus 
from the Triassic of California. The humerus of Baptanodon is not so broad as that 
of Shastasaurus but it shows greater specialization in the development of three un- 
equal facets on the distal end. 
The reduction in the number of intercentra in Baptanodon marshi, as well as in 
Baptanodon discus, appears to indicate the most specialized character of the genus. 
The separated zygapophysial facets in the cervical region, which become single in the 
vertebrxe more posteriorly, are approximated in the Ichthyosaurs. 
If Baur’s classification of the Ichthyopterygia be accepted the family Baptanodon- 
tidee proposed by Marsh would include the two genera Baptanodon and Ophthalmo- 
59Lydekker, &., Geol. Mag., Vol. I1., p. 309. 
* Baur, G., ‘‘ Ueber den Ursprung der Extremititen der Ichthyopterygia,’’ Bericht der XX. Versammlung der Ober- 
rhein. geol. Ver., Vol. XX. 
