LIASSIC FORMATIONS. 
121 
The fossils which have served in the present section of the Monograph have been 
obtained from the Lias of Lyme Regis and Charmouth. 
li . Ichthyosaurus acutirostris,^ Ow. Plate XXVIII, fig. 2. 
This species is so named from the slender, sharp-pointed form of the snout, unaccom- 
panied by such proportions of length as characterise the Ichthyosaurus tenuirostris and 
Ich. lonyirostris (ib,, fig. 3). 
The length or fore-and-aft diameter of the orbit in the subject of the above plate is 
6 inches, that of the part of the skull anterior thereto is 18 inches 7 lines. Both upper 
and lower jaws are impressed by a deep and narrow longitudinal groove near to and 
parallel with the alveolar border. The osseous sclerotic part of the eyeball occupies about 
two thirds of the long diameter of the orbit. 
The teeth are intermediate in character and in number between those of Ich. inter- 
medins and Ich. tenuirostris. 
The few trunk-ribs preserved in my present subject are slender, rounded, ungrooved, 
and have a feebly-produced anterior margin along their proximal fourth. 
The mesial border of the coracoid is sinuous, the articular surface for the episternum 
being better defined and more tumid than usual. The surface of the lateral or outer 
border for articulating with the scapula and humerus is strongly developed. The length 
of the coracoid in the specimen described is 7 inches, its breadth inches. 
The humerus is 7 inches in length and 5^ inches in breadth at the distal end. 
Of the fore paddle three digital series and a small portion of a fourth are preserved, but 
in such juxtaposition as to leave little doubt as to any considerable part of the fin-bones 
being lost. These, along the fore or radial border, including the radius, radio-carpal, 
and succeeding ossicle, are emarginate ; the rest have that border entire and moderately 
convex. After the fifth ossicle from the humerus the subquadrate merges into the trans- 
versely oval form. From the inclination of the radial digit toward the middle of the fin, 
a bifurcation is indicated at about the ninth ossicle from the humerus, and an irregular 
scattered series of small, full-elliptic, and circular bonelets, may be interpreted as an 
additional digit to the three normal ones, the more direct continuation of digit ii now 
extending down the centre of the bony paddle. An irregular ulnar series like that on 
the radial side is partially shown. If there shoukl be lack of osseous evidence of the 
breadth of the fore fin there is less of its length, which seems to have been two 
thirds that of the skull, and this is due rather to the size than the number of 
phalanges. The preserved basal portion of the left paddle repeats the character of the 
^ ‘Report,’ ut supra, p. 116. 
