CHELONIA. 



773 



broader than the hinder suture. The third costal sutures are sinuous and posteriorly- 

 divergent, while the fourth costal margins are the reverse, and nearly straight. The 

 second and third vertebrals are nearly of equal breadth, and the fourth is only a 

 little narrower than the last. The fifth is much broader than long, with a straight 

 truncated anterior margin, half as broad as its posterior margin. The caudal notch 

 is hardly perceptible. 



The gular suture is shorter than in B. lineata, equalling about one-third or one- 

 fourth of the post- gular suture. The latter almost equals the pectoral suture, which 

 is less than the two former sutures by about one-half of the gular sutiu-e. The 

 abdominal is the longest suture, but the preanal suture is shorter than the conjoint 

 gular sutures. The anal suture is less than the greatest breadth of one of its shields. 



I have not observed any very great disproportion between the males and 

 females of this species, but the largest specimen that has passed under my observa- 

 tion was a female from Kyouk Phyoo on the coast of Arracan, which greatly exceeded 

 the dimensions of any male, but stiU not to that degree that seems to prevail 

 in B. tliurgi, B. duvaucelli and some other species. 



The only structural difference that I can detect between the two sexes, is the 

 much greater length of the tail in the male, as compared with the female, which 

 is brought out in the accompanying table : 



Measurements of shells of B. baska, Gray. 



Length of carapace, straight line 



„ of plastron 

 Axillary breadth .... 

 Inguinal „ .... 



Greatest depth of shell . 

 Breadth of shell over curve, greatest 

 Length of caudal vertebrse 



16-75 

 15 00 

 5-75 

 5-75 

 6 75 

 16-20 

 4-90 



In adolescence, the nasal portion of the skull of the male is perhaps more 

 pointed and upturned than in the female at the same period. In youth, however, 

 the skull of the male is almost fiat (see PI. Ixxv^ figs. 6 to 10) as is shown 

 ia a specimen from the Irawady which has all the skull characters of this species, and 

 regarding the specific identity of which there can be no doubt. Unless the specific 

 characters of the adult are well ascertained, the young of such species as B. baska 

 and of other species of Batagur, owing to the great changes in form that take place 

 between youth and age in the shell characters, are very liable to be mistaken for 

 distinct species. I may also add that unless the characters which distinguish the 

 sexes are well known, similar errors are Hable to arise regarding them, and, moreover, 

 the sexes can only be satisfactorily determined by a direct appeal to the organs of 

 generation. 



The male, however, is distinguishable from the female by the remarkably 

 brilliant colouring of the front part of the body, but this is not always present, and 

 may perhaps depend on sexual periods. 



