82 MEMOIRS OF THE CARNEGIE MUSEUM 
Considering our limited knowledge of the structure of the Jurassic Ichthyosau- 
rians, I shall figure and describe this material in detail. 
The following description of the several elements is based largely on No. 878 
supplemented by such characters as are shown by Nos. 603 and 919. Unless other- 
wise stated the material should be considered as pertaining to No. 878. 
Tens Sy<wot, (ab WIU0G 3 3Hb JOC. Ines, eel AS Jeb, Wis il eiacl Ae lel, SIL, 
Figs. 1 and 2.) 
In general form the skull of B. discus bears a close resemblance to the other 
members of the Ichthyosauria. This is strikingly illustrated by the position and 
enormous size of the orbit, the presence of ossified sclerotic plates, the elongated 
nasals and premaxillaries and the reduced maxillaries. 
Seen from the side the skull” is triangular in outline. The anterior portion is 
formed by the elongated rostrum observed also in many of the European species. 
The orbital opening is a conspicuous feature of this aspect of the skull; it is very 
large and nearly circular in form; its greatest vertical diameter is 241 mm. the 
horizontal diameter being 234 mm. It is enclosed above by the post- and pre(?)- 
frontals, posteriorly by the postorbital, below by the jugal, and anteriorly, chiefly 
by the lachrymal. Just anterior to the orbit is the obliquely placed narial opening. 
In skull No. 603 these openings appear to be more nearly horizontal (see Pl. X., Fig. 
2) as is generally observed in Ichthyosaurus. The nares are bounded by the nasals, 
prefrontals (?), lachrymals, maxillaries, and premaxillaries. 
Viewed posteriorly (see Pl. XI.) the skull is subrectangular in form being wider 
than high. This aspect shows this region to be more compactly and firmly con- 
structed than in any known form of the Ichthyopterygia. The arrangement of the 
opisthotics and stapes is such as to give the greatest strength and rigidity to this 
region. ‘They act as braces from the basioccipital as a fixed point to all four angles 
of the skull. In comparing this view of the skull of Baptanodon with those of 
Ichthyosaurus as shown by Cuvier,'* Owen,'* Cope,” Frass,"* Bauer” and Woodward," 
12 All drawings of the skull with the exception of the inferior view, Plate IX., Fig. 2 (No. 603), have been 
made fron: specimen No. 878, though for the sake of completeness, elements and sutures not discernible in this speci- 
men, when present, have been supplied from No. 603. Whenever such use has been made mention is given in the de- 
tailed description of the elements to appear later. Dotted lines indicate the probable position of sutures not shown by 
the material at hand. 
13 Cuvier, R., ‘‘ Ossemens Fossiles,’’ Vol. 6, Plate X XIX. 
14Owen, R., ‘‘ Monograph of Fossil Reptilia of the Liassic Formations,’’ Pt. I1I., Plate XXVI. 
Cope, E. D., ‘‘On the Homologies of some of the Cranial Bones of the Reptilia,’’? Proc. Am. Assoc., Vol. XIX. 
fig. 2, p. 199. 
16 Frass, E., ‘‘ Die Ichthyosaurier der Siiddeutschen Trias und Jura Ablagerungen,’’ Plate II., figs. 3-8. 
17 Bauer, Franz, Anatomischer Anzeiger, Vol. XVIII., p. 586, fig. 17, 1900. 
18 Woodward, A.S., ‘‘Vertebrate Paleontology,” fig. D, p. 178. 
