38 DR. J. E. GRAY ON THE TRIONYCHIDjE. [Jail. 7, 



Holorhinal Birds. 



1. Impennes. 



2. Procellariidse. 



3. Colymbidee. 



4. Gallinae (excl. Pterocles and Turnix). 



5. Rallidae (excl. Parra). 



6. Otidse (inch (Edicnemus). 



7. Cariamidae. 



8. Psophiidse. 



9. Opisthocomidse. 

 10. Podicipidse. 



In his paper " On the Osteology of the Kagu," Mr. Parker, in 

 speaking of the nasal bone, says, " this part of the face is thoroughly 

 Gruine in both the Eurypyga and the Kagu ; the long open nasal 

 fossa, so sharp above at the bifurcation of the nasals, gives a 

 character to the face common to large groups of Grallse and 

 Palmipeds." Otherwise he does not employ this character in classi- 

 fication, as is evident when it is seen that he places the Kagu 

 close to Psophia and the Rails, which are holorhinal birds. 



It may be mentioned that the external nasal process of the nasal 

 bone is weak or obsolete in the struthious birds. 



5. Notes on Mud-tortoises (Trionyx, Geoffroy), and on the 

 Skulls of the different kinds. By Dr. J. E. G*ray, 

 F.R.S. &c. 



[Keceived Oct. 16, 1872.] 

 (Plate VIII.) 



The distinction of the species of this group of Tortoises is attended 

 with considerable difficulty, on account of the change of colour and 

 of the development of bones and of the callosities on their surface 

 during the growth of the animal. After considerable study, I am satis- 

 fied that the skulls, which appear to alter very little during the growth 

 of the animal, are among the best characters for the distinction of the 

 species, and division of them into groups ; but the study of these 

 parts has been attended with great difficulty, from the want of mate- 

 rials and so little being known of their development ; and it was not 

 until I had made one or two mistakes that I came to the con- 

 clusion that they afforded such good characters, and varied so little 

 during the growth of the species. 



The study of the skulls is attended with considerable difficulty, 

 from the want of specimens ; and the result has shown that the only 

 safe way of comparing them is actually by skulls with skulls. I at 

 first thought that it might be done by examining the mouths of ani- 

 mals in spirits or dry ; but the skin on the side of the mouth hides 

 so much of the skull, and gives the palate quite a different character 

 from that which exists in the skull : and the examination of the mouth 



