1871.] HIJLKE KIMMEEIDGE ICHTHYOSATTEUS. 441 



on one another. The first forty-five bear a double costal tubercle, 

 and the remaining centra have a single one. The fifth, sixth, and 

 seventh centra are each -8 inch long ; the fifteenth is rather less 

 than '9 inch. The vertical and transverse horizontal diameter 

 cannot be accurately taken. The length of the hindermost centra 

 is rather under -8 inch, while their transverse horizontal diameter 

 exceeds that of any of the preceding ones. The ribs do not offer 

 any thing peculiar ; towards their vertebral end they are compressed 

 and channelled ; in the flank they have a cylindrical form ; and their 

 ventral ends are flattened. 



A pair of flat bones going below the early thoracic ribs are, I 

 infer, from their position, and from their close association with the 

 scapulae, the coracoids. Their form is unusual. They are much 

 more elongated in the direction of the trunk's axis than are those 

 of the Liassic IcJithyosauri with which I have had an opportunity of 

 comparing them, their axial diameter being to their transverse one 

 as 5-3 : 2-8 inches. "With this greater length their anterior border 

 reaches much further forwards in advance of the glenoid cavity than 

 in the Liassic forms ; and it, as also the median border, is straight, 

 so that the latter touches its fellow throughout its whole length 

 when the two coracoids remain naturally united, as they do in this 

 instance. The articular end of the scapida is unusually broad. 



The paddles, particularly the hind ones, are extremely reduced. 

 Their precise form and composition cannot be learned ; for most of 

 the lesser bones are missing. The humerus is 2*7 inches long, its 

 distal end is 2-1 inches broad, and the diameter of its middle is ]*6 

 inch. The femur is only 2 inches long ; its proximal end is 1*4 inch 

 broad, its distal end is 1*1 inch, and the diameter of the middle is 

 •9 inch. 



This, as I believe, new species, which I propose to call /. enthe- 

 Tciodon, resembles in the slenderness of its snout the two Liassic 

 species /. longirostris and I. tenuirostris, but it is readily distinguish- 

 able from these by the following characters. Its snout, relatively to 

 the length of the cranium, is not so long as that of /. longirostris ; its 

 smaller tooth-root is smooth, and not distinctly fluted as in /. tenui- 

 rostris; the shape of its coracoid is quite different from that of 

 the coracoid of tenuirostris ; and its spinal column is much stouter 

 than that of either of these species. It resembles both /. tenuirostris 

 and /. longirostris in the preponderence of its fore paddles over its 

 hind ones ; but its fore and hind paddles, so far as I can judge of 

 their size by that of their proximal bones, are very much smaller ; 

 indeed the paddles, relatively to the whole skeleton, are smaller 

 than in any other species known to me. 



EXPLANATION OP PLATE XVII. 



Skeleton of Ichthyosaurus entheJciodon from Kimmeridge Bay, one twelfth 

 natural size. 



