138 Bibliographical Notices. 



is now represented by one or two species peculiar to the great rivers 

 of India, more especially the Ganges ; and the fossil diifers from 

 both the Gavialis gangeticus, Auct., and from the perhaps nominal 

 G. tenuirostris, Cuv., in the form and relative size of the teeth." 



In the interesting observations on the cretaceous fossil reptiles, 

 Prof. Owen describes a new species of Mososaurus, M. gracilis, and one 

 of Plesiosaurus, P. Bernardi, and also satisfactorily establishes two 

 genera of lizards, Coniasaurus and Dolichosaurus, with procoelian 

 cup-and-ball vertebrae, by the recent discovery of portions of the jaws 

 and teeth : of one of these which is distinct from the Raphiosaurus, 

 Prof. Owen remarks, " There is no existing species of the Iguanian or 

 other herbivorous family, nor any of the pleurodont saurians with 

 which the present chalk fossil is identical, nor can I refer it to any of 

 the established genera of Lacertia : the absence of the cranium and 

 bones of the extremities does not allow of any closer comparison with 

 the Monitors, Iguanas, or Scinks ; but the characters of the teeth 

 justify the consideration of the fossil as the type of a hitherto un- 

 described genus and species, which I therefore propose to call Conia- 

 saurus crassidens, or the thick-toothed lizard of the chalk forma- 

 tion." Of the other, a beautiful specimen, comprising the head and 

 anterior thirty-six vertebrae, in the collection of Mrs. Smith, and a 

 chain of posterior abdominal and sacral vertebrae belonging to Sir P. 

 Egerton, which there is good reason to suppose belonged to the same 

 individual, Prof. Owen gives a detailed description, and shows in 

 conclusion, " That all the general characters of the Lacertian type 

 of the vertebrate skeleton are presented by the Dolichosaurus ; they 

 are most modified in the cervical region, where the Ophidian type is 

 rather followed, in the number and size of the vertebrae, and in the 

 size and shape of the ribs ; a less decided approach, but one still in- 

 dicating an affinity to the Ophidians, is made by the unusual length 

 of the slender trunk, which includes, from the skull to the sacrum, 

 not fewer than fifty-seven vertebrae, and is not less than 1 8 inches in 

 length. The smallness of the head accords with the long and slender 

 proportions of the neck, and must have added to the snake-like ap- 

 pearance of this early example of procoelian lizard. But the com- 

 plete and typically Lacertian organization of the scapular and pelvic 

 arches, and of their locomotive appendages, proves that the Dolicho- 

 saurus was more strictly a lacertine Saurian than the existing genera, 

 Pseudopus, Bipes, and Ophisaurus, which effect the transition from 

 the lizards to the snakes or typical Ophidian reptiles." 



The Fishes of the Chalk are interesting, inasmuch as here first ap- 

 pear forms belonging to those two orders of fishes, the Cycloid and 

 Ctenoid, which attain their maximum development in the present 

 seas, and associated with the Placoid and Ganoid orders, which are 

 characteristic of the older formations. Of the Placoid are two new 

 genera, Aidodus and Plethodus, and several new species belonging to 

 the genera Ptychodus, Acrodus, Corax, and Oxyrhina ; but the most 

 interesting are the remains of a Cestracion, as — 



" The discovery of a species of true Cestracion in the Chalk is an 

 event of much interest, since this genus has hitherto only been known 



