326 Dr. J. E. Gray on the Miid- Tortoises of India. 



EXPLANATION OF PLATE XY. 



Fig. 1. Blysmia rtiJicolHs ( $ ). 



Fig. 2. Phocylides collnris (c?). 



Fig. 3. Achrionota hilineata ( c? ). 



Fig. 4. lonthocerus ojMhalmicus (J); 4 a, right fore leg. The hairs on 

 the antennae are too delicate to be represented in a figure of this 

 size. 



Fig. 5. Prophthalmus planvpennis ( cJ ). 



Fig. 6. sanguinalis {S). 



Fig. 7. Cor (Ins semipunctatus {S)'i 7cr, head and antennpe, side view. 



Fig. 8. Evpsalis promissus (c?)- The antennae are not sufficiently accu- 

 rate as regards the last five joints. 



Fig. 9 a. Hend oi A7norphoc('phahis, s^. nov. ($), (prothorax canalicu- 

 late); 9 h, head o{ A7n()rphocephalus, ST^. nov. (5), (prothorax 

 not canaliculate, allied to A. australis, Lac). 



Fig. 10 a. Side view of the head of A^norphocephalus sideicoUis ( J ) ; 

 10 b, ditto, top view. 



Fig. 11. Side view of the head of Cordus hosiyes, Germ., for comparison. 



Fig. 12. Head and antenna of Prophthalmus sanguinalis ( $ ). 



Fig. 13. Head and Bnierma. oi Stratiorrhina xiphias (c?),Westw. (A)'r he- 

 nodes). 



XL VII. — Notes on the Mud- Tortoises of India (Trionyx, 

 Geoffroy). By Dr. J. E. Gray, F.R.S. &c. 



The Tliree-clawed or Mud-Tortoises are a very natural and 

 well-defined group ; but the division of them into species 

 has been a subject of great difficulty to European zoologists, 

 chiefly arising from the very imperfect material which they 

 have had at their command. 



Formerly Geoffroy, Bell, and Fitzinger seem to have re- 

 garded the extent of the union of the ribs as a character of a 

 species ; the latter even attempted to divide them into genera 

 from characters derived from this part. But it is now well 

 understood that the extent to which the ribs are united de- 

 pends entirely upon, the age of the animal, the union being- 

 only partial in the young, and entire in the adult, as in i\\Q 

 land tortoises and terrapins. 



The number, extent, and shape of the sternal callosities no 

 doubt afford very good characters for the distinction of the 

 species, if adult animals are compared together ; but they are 

 gradually developed, and in some species (or perhaps in some 

 individuals of the same species) they are much later developed 

 and much longer in coming to their perfect state than they are 

 in others. This is also the case with the development of the 

 odd bone in front of the dorsal disk ; so that these parts can 

 only be used as characters when specimens of \\\q. same age 

 and stage of development are compared, and especially speci- 

 mens which liave arrived at their adult state. 



