48 VEKTEBRATA. 



No. 68. [207J Ichthyosaurus intermedius, Couyb. 



Skeleton, on slab (cast). The Ichtbj'osaurs are distinguished by a long 

 head, short neck, large abdomen, polydactylous paddles, and a powerful finned 

 tail. They have a single occipital condyle; one vomer; thin, biconcave, ossi- 

 fied vertebrae; stout, conical, striated teeth implanted in a common alveolar 

 groove; a large eye with a compound circle of overlapping sclerotic plates. 

 The general form of the cranium resembles that of the Dolphin; the essential 

 difference lies in the small size of the cerebral cavity, in the vast depth and 

 breadth of the zygomas, and in the distinctness of the cranial bones. The 

 mouth is very wide, and the jaws are armed with numerous teeth, indicative 

 of a predatory and carnivorous nature. The lower jaw is made up of twelve 

 pieces. The scapular arch resembles that of the OrnithorhyncMis, and gave 

 great strength to the chest and paddles, permitting the animal to crawl on the 

 sea-shore — a thing impossible to the mammalian sea monsters. The vertebrae 

 number over an hundred, and the end of the tail was flattened vertically, and 

 lengthened out as in the Crocodiles. The very frequent displacement of the 

 caudal vertebrae, about one-fourth of the way from the extremity, is owing to 

 the perishable caudle fin falling over as the animal dies. The Ichthyosaurus 

 was probably naked like the Whale, but carried a prominent ridge on the 

 dorsal surface, like that of the male Pond-Newt. When full-grown, it may 

 have reached the length of forty feet. Of no extinct vertebrata are the ma- 

 terials for a complete and exact restoration more abundant and satisfactory 

 than of the Ichthyosaurs. This species is the most common form, but has 

 not been found over nine feet in length. This splendid specimen, now in the 

 British Museum, was discovered by Thomas Hawkins in the Lias at Street, 

 near Glastonbury, England. The cranium and jaws, spinal column gently 

 arched, and the four entire paddles, are very perfect!}' represented. Accord- 

 ing to Hawkins, there are one hundred and ten teeth in the upper jaw, and 

 one hundred in the lower; one hundred and eleven vertebrae; thirty-nine ribs: 

 niuety-five bones in the anterior paddle, and thirty-nine in the posterior. 



Size, 9 ft. lin. X 2 ft. 11 in. 



No. 69. [310] Ichthyosaurus platyodon, Conyb. 



Head (cast). This species is one of the most gigantic of Ichthyosaurs, 

 attaining the length of thirty feet. It derives its name from the crown of the 

 tooth being more flattened than in other species. The bodies of the vertebrae 

 are also more compressed. The head is relatively larger than in Ichthyosaunts 

 communis ; the lower jaw is remarkablj' massive and powerful, and projects 

 backwards beyond the joint, as far as it does in the Crocodile. The fore and 



