176 POURTII REPORT — 1834. 



aware that much addition has been made to our knowledge of 

 this group. Nevertheless there is great need of further exami- 

 nation in order to determine the value of those characters which 

 have been hitherto employed in distinguishing the species. It 

 may reasonably be questioned whether these have not been over- 

 miUtiplied, from placing too great reliance upon slight differences 

 in the form and number of the nuchal, cervical, and dorsal plates. 

 I may mention a memoir by Geoffroy on the Gaviah, as more 

 recent than his others, published in 1825*, in which he has 

 treated largely of their organization and affinities. He consi- 

 ders the former as offering sufficient peculiarities to warrant the 

 establishing of a distinct genus of this group, which Cuvier re- 

 garded as merely a subgenus of Crocodilus. 



The Saurian Reptiles have been much attended to by Mr. 

 Gray. In the Ann. of Phil, for 1827 1, he has given a synopsis 

 of tlie genera belonging to this group. In a subsequent paper 

 published in the same volume J he has made some additions 

 and corrections to his first communication. He has made it a par- 

 ticular object to revise the species of Chamcsleon. To M. Milne 

 Edwards we are indebted for a paper in the Ann. des Sci. for 

 1829§, which though relating only to the restricted genus Xo- 

 certa, may be found valuable in a general point of view from 

 the remarks which it contains on the zoological characters of 

 this group. Those who have studied these reptiles know what 

 difficulty attends the discrimination of species. Milne Edwards 

 has sought to remove this difficult}'. He has ascertained that 

 in this geiuTS the best distinguishing characters are derived from 

 the different kinds of scales, more especially the large squamous 

 plates which cover the upper part of the head. He particularly 

 dwells on the relative size of the occipital and parietal plates, 

 and the forms of the scales between the eye and the ear||. He 

 does not place much reliance on the character derived from the 

 number of femoral pores, which he finds often varying in the 

 same species, although considered as constant by Merrem and 

 Blainville. In the same voliune with the above memoir is one 

 by M. Duges, treating partly of the same subject ; and it is sa- 

 tisfactory to find that he confirms what Edwards says respect- 

 ing the characters of the scales. It may be observed that Wagler 

 appears to have derived much assistance from the teeth in cha- 

 racterizing both the Emydosavrian and Saurian Reptiles. In 

 one portion of his work he has treated of this subject in great 



* Mem. du Mus., torn. xii. t vol. ii. N.S. p. 54. 



X p. 207. § torn. xvi. p. 50. 



II Merrem and others had previouslj' availed themselves of these characters, 

 but according to Edwards, they have not made a judicious use of them, or se- 

 lected those scales on which any reliance can be placed. 



