508 DR. J. E. GRAY ON THE GENUS EUCHELYMYS. [Mar. 19, 



both in the outline of the thorax and in the convexity of the back 

 very considerably. The smallest is the broadest, with the back of 

 the shell much elevated in the centre. Indeed no two of the speci- 

 mens are alike in form and convexity, which induces me to believe 

 that they all belong to one variable species. 



** Thorax oblong, convex, high. Head large. 



3. Chelymys krefftii. (Plate XXVIII.) B.M. 



Thorax oblong, scarcely broader behind, very convex. The second, 

 third, and fourth vertebral shields as long as or rather longer than 

 broad ; the second and third nearly square, with only a slight angle 

 near the middle of each side ; the fourth contracted behind ; the first 

 nearly square, rather broader than long, and rather broader in front. 

 Thorax convex, elevated from the margin, the lateral processes convex. 

 Head large, above olive, with a broad white streak from the back of 

 the orbit to the upper front margin of the tympanum ; a broad white 

 streak from the angle of the mouth to the lower part of the tym- 

 panum. Beaks very strong and convex. Upper part of neck slightly 

 granular. 



Chelymys krefftii, Gray, Ann. & Mag. Nat. Hist. 1871, viii. 

 p. 336. 



Hah. Burnett River. 



One specimen (Krefft's MS. no. 9) is coloured very much like the 

 others received from Mr. Krefft, but differs in being oblong and very 

 convex, instead of being broadly ovate and much more depressed, and 

 in the form of the vertebral plates. It also differs in having a much 

 larger head compared with the size of the body. 



It has been suggested that this may only be a difference of sex ; but 

 it is very curious that, out of a large series, it should be the only one 

 of the sex that has come to us. 



2. Euchelymys. 



Head covered with a continuous soft skin, which is reticulated over 

 the temporal muscles, with an oblong, triangular, diverging hard 

 plate on each side of the occiput. Chin with two beards. Back 

 of the neck netted, slightly tuberculated or convex. Forehead and 

 crown nearly square, scarcely dilated behind ; hinder edge of occiput 

 scarcely sinuated. Thorax convex, solid ; cavity contracted in front ; 

 nuchal shields narrow, well developed ; vertebral shields broad, the 

 fifth as broad as or broader than the others. Fore legs with large 

 transverse scales in front and with keeled scales on the outer margin. 



Euchelymys (part.), Gray, Ann. & Mag. Nat. Hist. 18/1, viii. 

 p. 118. 



I first established this genus in the * Annals and Magazine of 

 Natural History' for August 18/1, placing the two species together, 

 because they both had nuchal plates ; but I believe now that the 

 second species was founded on an abnormal specimen of Elseya. 



