20 



CHELONIA. 



The sculpture of the nuchal is finer than that of the costal from the 

 London Clay on which T. pustulatus, Owen \ was founded. The 

 sculpture of the seventh costal from Bracklesham figured in Dixon's 

 ' Geology of Sussex/ pi. xii. fig. 15, which very probably belongs 

 to the present form, is also different from that specimen. The 

 nuchal resembles that of T. stiriacus, Peters 2 , from the Middle 

 Miocene of Styria ; but the much lower horizon of the present form 



Fig. 4. 



Trionyx bowerbanki. — Nuchal bone ; from the Middle Eocene of Bracklesham. 

 £. In the figure on the right the sculpture is shown of the nat. size. 



indicates of itself in all probability a specific distinction, and the 

 hypoplastral mentioned below is decidedly different from that of 

 T. stiriacus, in which the costals have a ridged sculpture. 

 Hab. Europe (England). 



38960. The nuchal bone, slightly imperfect anteriorly ; from the 

 (Fig.) Middle Eocene of Bracklesham, Sussex. The type spe- 

 cimen ; figured in the accompanying woodcut. This 

 specimen, which appears to be adult, indicates a compara- 

 tively small species, agreeing approximately in size with 

 T. hurum. Bowerbank Collection. Purchased, 1865. 



33198. The right hypoplastral of a small subadult Trionyx probably 

 (Fig.) belonging to this species ; from Bracklesham. Figured 

 by Owen in his ' Beptilia of the London Clay, &c.' pt. i. 

 pi. xix. d. fig. 7 (reversed). The nature of the sculpture 

 agrees fairly well with that of the nuchal, but the contour 

 of the inferior border differs markedly from that of the 

 hypoplastral of T. styriacus figured by Peters, ojj. cit. 

 pi. vi. figs. 3, 4. The inner surface of the greater part of 

 the outer buttress is broken away, but the base of this 

 buttress has the marked thickness of the American forms 

 described as Plastomenus. 



Dixon Collection. Purchased, 1851. 



1 Keptilia of the London Clay, &c. (Mon, Pal. Soc), vol. i. pt. i. p. 60, pi. 

 xix. b. figs. 7, 8 (1840). , 



2 Denksclir. k. Ak. Wiss. Wien, vol. i.\. pt. ii. p. 12, pi. vi. fig. 2 (1855). 



