424 Dr. A. Giiutlier on Hydromedusa. 



Matamata, and in other respects of the Platemys tuherosa 

 from British Guiana, which, however, is sufficiently distinct 

 to be placed in the genus Platemys, as proposed by Peters. 

 The shell is depressed, with a short oval outline, the hind 

 margin being very obtuse. Each vertebral scute is raised 

 in the middle into a tubercular prominence, and each costal 

 is likewise provided with a similar prominence on its 

 areola. The tuberosities of the marginal scutes are in the 

 form of oblique ridges which terminate in a prominence 

 at the posterior corner of each scute. Tubercular ridges 

 radiate also from the areolar part of each vertebral and 

 costal scute, so that the whole surface of the shell presents 

 an extremely uneven appearance, resembling that of a rough 

 stone. 



Although there are six scutes along the vertebral line, 

 the first of which is very little smaller than the second, 

 and does not enter the margin of the shell, this genus does 

 not differ in this respect from other turtles. That first scute 

 is evidently only a very large nuchal shield which has been 

 excluded from the margin by the enlarged foremost pair of 

 marginals. If this were not the case, the number of costals 

 would be increased too, and we should then have five of 

 them instead of four. 



The sternum is flat, much longer than broad, truncated in 

 front and deeply notched behind, the margin forming an 

 angular edge along the bridge connecting the sternum with 

 the upper shell. The bridge is rather narrow, formed only by 

 ]iart of the abdominal and pectoral scutes, which are suturally 

 connected with the fifth, sixth, and seventh marginals, in- 

 guinal and axillary scutes being absent. The median gular 

 is large and very long, separating not only the gulars proper, 

 but also nearly the postgulars. Abdominal rather narrower 

 than the pectoral and the postabdominal ; caudals large, two 

 thirds the size of the postabdominals. 



Neck long, bending towards the right and covered with 

 granular skin, some of the granules on the sides being pointed j 

 head flat, long, with short snout and short pointed nose, 

 covered with soft skin, in which, however, the division into 

 a great number of small scutes is distinctly indicated. Tym- 

 panum not visible ; eyes of moderate size, with round pupil, 

 close together, and partly directed forward. The snout is 

 scarcely longer than the eye ; nostrils small, round, directed 

 forward. Jaws weak and narrow, covered with a horny 

 sheath, the cleft of the mouth extending as far back as the 

 eye. A broad fold at the angle of the mouth permits the gape 

 to be opened wide in a vertical direction, and the numerous 



