254 MKMOILS OF THE QIKEXSLAND MLSEUM. 



-which were cemented to the lateral surface of the rostrum are shown in Plate XVI.. 

 Between the mandibular rami ahout the mid-region of the skull there h a brecoiated 

 mass formed mainly of broken teeth, although containing other fossils. Ths teeth 

 are subcylindrical, and there are no anterior or posterior carinae. They are about 

 55 mm. in length, with a maximum diameter of 18 mm. After counting the number 

 of grooves on exposed contours, it is considered that a perfect specimen would have 

 about thirty longitudinal striae. The teeth are evenly conical, and there is no- 

 marked tumidity at the alveolar border. Judging from the numerous fragments, 

 thev A\ere fairly isodont, but some of the roots are decidedly compressed. They 

 are somewhat larger than those in the type specimen in this Museum of 

 Ichthyosaurus marathonensis, Etheridge fil. It is estimated that about forty teeth 

 were present in each alveolar groove. 



On the posterior third of the lower jaw, and cemented thereto, may be seen 

 remains of the stout, cyUndrical " hyoid rods " (to use Sollas' term). These are 15 

 mm. in diameter, and attain a length of 250 mm. They also overlap the lateral 

 surface on the left-hand side, as may be seen in Plate XV. 



Unfortunately no other remains were found in association with the skull, and 

 although this Museum contains several specimens of vertebrae, a paddle, and a few 

 other fragments from Western Queensland Cretaceous formations, it would be 

 unAvise to describe these in conjunction with the present material. 



Classification. — The Ichthyosauria have been divided into four families : — 

 Mixosauridce, Ichthyosauridce, Baptanodontidce, and Shastasauridce, the last-named 

 being added by Merriara in 1902.21 The diagnostic characters of the majority of 

 recent genera are not founded on cranial characters. It is evident, however, that 

 our fossil has no affinity, generically, with the Ophthalmosaurus-Baptanodon group 

 (Jurassic), which is characterised by an enormous eye and a very reduced dentition. 

 Neither is it related to Mixosaurus (Triassic), in which the teeth are not set in a 

 continuous groove. In the occipital and mandibular regions and in the basis cranii 

 the elements in the Queensland skull approximate to the Ichthyosaurus type, but 

 apparently unique characteristics are present on the superior surface of the skull. 



Two species of Ichthyosaurus have been described from fragments obtained 

 in the Cretaceous deposits of Western Queensland. In 1867, McCoy briefly described 

 Ichthyosaurus australis^^ and in 1869 supphed some additional details. ^^ His material 

 consisted of two portions of the skull, teeth, some dorsal vertebrae, paddles, and 

 a humerus, radius, and ulna, and his short description was not illustrated. In 1888, 

 Etheridge^/. described Ichthyosaurus marathonensis^'^ from a maxillary and dentary 

 section ten inches in length, which is now in the Queensland Museum. In 1892 



21 Merriam, Bull. Dep. Geol., Univ. Calif., Vol. Ill, 1902, p. 87. 

 "McCoy, Ann. Mag. Nat. Hist., XIX, 1867, p. .355; XX, p. 196. 



23 McCoy, Trans. & Proc. Roy. Soc. Vic. IX, 1869, pp. 77-78. 



24 Etheridge, Pr. Linn. Soc. N.S.W., III, 1888, p. 405,. PI. VII. 



