TKIONYCH.IDJB. 19 



30409 a. The inner portion of the conjoint left hyo- and hypoplas- 

 (Fig.) trals of an adult Trionyx which, from its comparatively 

 coarse sculpture, probably belongs to the present species ; 

 from Hordwell. Described and figured by Owen, op. cit. 

 p. 59, pi. xix. d. fig. 6. The absence of projections on the 

 inner border is due solely to the age of the specimen. The 

 degree of rugosity of the sculpture bears the same relation 

 to that of the carapace as is the case between the 

 corresponding portions of the shell of Chitra. In its 

 relatively large antero-posterior diameter, and in the 

 thickness of the commencement of the outer buttress of 

 the hypoplastral, this specimen approximates to the 

 description of the forms referred to Plastomenus. 



Hastings Collection. 



** Trionyx rivosus, Owen \ 



Probably the young of the preceding species. 



Known only by the carapace of a young individual, which is 

 characterized by the presence of a few bold sinuous longitudinal 

 ridges, which are much more prominent than the rest of the 

 sculpture. In this respect the specimen resembles the young of the 

 existing T. cartilagineus 2 , and also some of the American fossil 

 forms figured by Cope 3 as Plastomenus. Traces of similar sculpture 

 remain in the eighth costals of T. planus, No. 30410 (p. 18). 



Hab. Europe (England). 



30405. The posterior part of the carapace of a young individual ; 



{Fig.) from the Upper Eocene (Lower Oligocene) of Hordwell, 

 Hampshire. The type ; described and figured by Owen 

 in his ' Reptilia of the London Clay, &c.,' pt. i. p. 56, 

 pi. xviii. a. figs. 1,2; it shows the last five costals and 

 the sixth neural. Hastings Collection. Purchased, 1855. 



Trionyx bowerbanki, Lydekker, n. sp. 

 Very imperfectly known. Nuchal bone emarginate, with the 

 sculptured portion convex, and sharply differentiated by a prominent 

 ridge from the non-sculptured portion ; sculpture in the form of 

 small pits, arranged in lines near the periphery. The hypoplastral 

 provisionally referred to this species has a very thick outer buttress. 



1 Eeptilia of the London Clay, &c. (Mon. Pal. Soc), vol. i. pt. i. p. 56 (1849). 



2 =T. ornatus, Giinther, ' Eeptilia of British India,' pi. vi. fig. B. 



3 Tertiary Vertebrata of the West (Rep. U.S. Geol. Surv. Terrs, vol. iii.), 

 pi. xviii. figs. 9-12. 



C2 



