LIASSIC FORMATIONS. 
109 
subservient to the support and movements of the tongue tlian to the mechanism for 
defending the larynx and pharynx from the entry of water during the struggles of a 
submerged prey, when the mouth of the air-breathing destroyer is necessarily exposed to 
the free ingress of the aquatic medium. The condition of the hyoid apparatus in the 
Icldliyosauriis indicates that its tongue may have been but little better developed than in 
the Crocodile, and, since the Ichthyosaur obtained its food under the same eircumstances 
which necessitate the hyoid and lingual modifications in tlie Crocodile, it may be inferred 
that the hyoid arch was physiologically related to the working of a similar valvular 
apparatus for defending the orifice of the air-tube from the water admitted into the 
mouth during the capture of the fishes, the remains of which have been found in the 
region of the alimentary canal of the great Sea-lizards, 
The modifications of cranial structure of the known kinds of Ichthyosaurus are 
chiefly presented by the upper and lower jaws, which become elongated and attenuated 
in degrees exemplified by the species next to be described. With these modifications are 
associated increase of number with decrease of size of the teeth, and their total dis- 
appearance, finally, as in the Ichthyosauroids of the upper Jurassic beds of Wyoming and 
some other American localities. For these edentulous Ichthysaurs, their discoverer. 
Prof. Marsh, has proposed the generic name Bauranodon j ’ it is probable that, as in the 
case of Cetacea, showing minor modifications than do the toothed Ichthyopteryyia, other 
generic terms for some of these species may be proposed. 
C. Species. 
a. Ichthyosaurus breviceps, Ow., Plate XXIX. 
In the skeleton of this species (PI. XXIX, fig. 2) the skull is almost equally divided 
between the antorbital part and that behind ; it is about one sixth the length of the 
entire body, as represented by the vertebral column. Tliis includes, in the specimen 
figured, 125 vertebrae, of which 46 lie between the skull and pelvis. The neural spines 
of such trunk-region are lofty, equalling along its major part the vertical diameter of 
the rest of the vertebrae taken from the base of the spine. The intervals between the 
spines are very narrow. The centrums are largest at and near the pelvic region. The 
fore fin has five normal digital series, with smaller supplementary ossicles along both 
fore and hind borders ; it is twice as long and as broad as the hind one. 
The specific characters are more fully exemplified in specimens of the skull of larger 
individuals, which show that the proportions of the rostrum to the rest of the skull in 
the smaller skeleton may be due to nonage, but the cranial conformation is the same. 
^ ‘American Journal of Science,’ vol. xvii, p. 85, January, 1879; ib., vol. xix, p. 169, February, 
1880. 
