ICHTHYOSAURI!)^. 83 



Ichthyosaurus tenuirostris, Conybeare 1 . 



Syn. Ichthyosaurus chirostrongulostinus, Hawkins 2 . 

 Ichthyosaurus grandipes, Sharpe 3 . 

 Ichthyosaurus sinuatus, Theodori 4 . 



Cranial rostrum very long and slender, and in the adult exceed- 

 ing four times the diameter of the orbit ; supratemporal fossa in the 

 form of an equilateral triangle (compare fig. 33) 5 ; fronto-nasal 

 region comparatively broad and flat, narrowing gradually towards 

 rostrum, and lateral borders of frontal aspect of nasals rounded in 

 front of orbits ; parietals forming a broad flat bar between supra- 

 temporal fossae. Jaws completely toothed. Pectoral limb (compare 

 fig. 32) comparatively short, with anterior border of radiale either 

 notched or entire, but that of adjacent carpale of second transverse 

 row always entire ; and all the bones very large, more or less 

 polygonal, and those of the first longitudinal ulnar row not distinctly . 

 oblong. Humerus with slender shaft and much expanded distal 

 extremity. Scapula with proximal border much rounded, and with- 

 out prominent anterior ridge on dorsal surface. The radius (fig. 25) 

 has the vertical diameter almost as long as the transverse ; and 

 usually articulates by a long facet with the ulna, so that the facet 

 for the intermedium becomes much reduced, and the ulnar border 

 is consequently nearly straight. The radius and ulna frequently 

 anchylose with one another, and sometimes also with the adjacent 

 bones ; and a small circular vacuity generally remains between the 

 two. The relative length of the rostrum seems to have increased with 

 age. A skeleton in the Museum of Practical Geology, from Street, 

 shows that the contour of the facial profile was not dissimilar to 

 that of the next species. 



This species does not appear to have attained very large dimen- 

 sions ; and occurs in both the Upper and Lower Lias. 



Hah. Europe (England and Wiirtemberg). 



R. 1120. Slab showing the dorsal aspect of a nearly entire skeleton ; 



(Fig.) probably from the Lower Lias of Lyme-Regis, Dorsetshire. 



Figured by Owen in his 'Liassic Reptilia' (Mon. Pal. 



1 Trans. Geol. Soc. ser. 2, vol. i. pt. i. p. 108 (1822). 



2 Memoirs on Ichthyosauri, &c. pi. xvi. (18o4). 



3 Proc. Geol. Soc. vol. i. p. 222 (1830). 



4 Beschreib. des Ichthyosaurus triyonodm, p. 50, Munich (1854). — As a 

 variety. 



5 /. latifrons is so closely allied to this species that the figures of this part of 

 the skull and of the pectoral limb of the latter may be compared with this 

 description. 



G 2 



