122 REPORT — 1839. 



tenuirostris, although when a series of them are compared with 

 a corresponding series of the tenuirostris, they are seen to 

 be upon the whole a little wider at their base in proportion to 

 their length. The most marked difference between these species 

 is the length of the jaws ; the intermaxillaries aiid dentary 

 pieces being intermediate in this respect between the Ich. inter- 

 medins and Ich. tenuirostris. 



The best example of the remains of the Ich. acutirostris which 

 I have yet seen, is in the museum of the Natural History So- 

 ciety of Lancaster. It gives a profile view of the entire head, 

 and of one anterior paddle. 



The length of the head is eleven inches ten lines, and the 

 alveolar dental series extends six inches six lines along the 

 border of the jaws. The vertical diameter of the entire skull 

 anterior to the orbit is three inches, and from this point 

 both the upper and lower jaws regularly converge, in almost 

 every direction to the end of the snout, which is sharper and 

 more spear-shaped than in the other species. 



The teeth vary in length from three to five lines, and about 

 twenty-four may be counted in the space of three inches ; they 

 present a more regular alternation in length than I have ob- 

 served in the other species of Ichthyosauri. There are about 

 fifty teeth on each side of the upper, and forty on each side of the 

 lower jaw, in all about 180 ; they are slightly bent backwards. 



The orbit is relatively smaller than in the Ich. tenuirostris, 

 but wider than in the Ich. intermedius ; its inferior and posterior 

 boundaries are thicker than in the Ich. tenuirostris. 



I have not been able to found any characters on the structure 

 of the vertebral column in the Ich. acutirostris. The humerus 

 is relatively as long as in the tenuirostris, but is less expanded 

 at the distal extremity. The radius presents the same anterior 

 emargination as in the tenuirostris and platyodon. The phalan- 

 gial ossicles are of an irregular rounded form, and are arranged 

 in four digital series, presenting an arrangement as well as a 

 relative size, which is intermediate between those which cha- 

 racterize respectively the Ich. tenuirostris and intermedius. 



Mr. Hawkins has figured two snouts apparently belonging to 

 this species in PI. XIV. of his Memoirs, one of which, the 

 larger and more complete specimen, was from the lias-quarry at 

 Street, the other from that at Walton. 



Besides the localities indicated in the preceding description, 

 remains of the Ichthyosaurus acutirostris occur in the lias for- 

 mation at Boll in Wirtemberg. 



Ichthyosaurus latifrons, Koenig. (Icones Sectiles, pi. xix.) 



This species is founded on a specimen in the British Museum, 

 including a portion of the cranium, of which the anatomy 



