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. 



h. Ichthyosaurus acutirostris, 1 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. longirostris (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- 

 medius 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 7^ 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 n now 

 extending down the centre of the bony paddle. An irregular ulnar series like that on 

 the radial side is partially shown. If there should 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 



1 'Report,' ut supra, p. 116. 



