EEPTILIA. 



57 



Enaliosaurian s . 



No. 207. Ichthyosaurus intermedius, Conyb. 



5 



■ ^ .;■■ , , , ' -' ' ' 



p us 



Skeleton, on slab. The Ichthyosauri 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, ossified 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 dis- 

 tinctness 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 

 Ornithorhynchus, 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 ex- 

 tremity, is owing to the perishable caudal 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 Ichthyosauri. This species is the most common form, but has not been found over 

 seven feet in length. It derives its specific name from the intermediate character 

 of the teeth, which are more acutely conical than in i". communis, and the striae 

 less prominent ; but are less slender than in I. tenuirostris. The maxillary portion 

 of the skull is relatively shorter, and converges more regidarly to the snout than 

 in I. communis ; and the teeth are longer, more slender and numerous. 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 per- 

 fectly represented. According 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 ; ninety-five bones in the anterior paddle, and thirty - 

 nine in the posterior. Size, 9 ft. 1 in. x 2 ft. 11 in. Price, $20.00. 



No. 208. Ichthyosaurus intermedius, Conyb. 



Part oe the Skull with the eye and sclerotic plates deeply dissected out. 

 It was found in the Lias at Lyme-Regis, England, and is in the Garden of Plants. 



Size, 10x8. Price, $3.50. 



