1. CINOSTERNUM. 35 
The rib-like process of the nuchal is long and situated behind 
the marginals in the young, short and extending below the first 
marginal in the adult. Neural plates narrow, forming an incom- 
plete series, five or six in number, the two or three last pairs of 
costals, and sometimes also the first pair, in contact on the median 
line; eighth costal sometimes (C. odoratum, C. scorpioides) very 
small, and without distal point. Vertebral and costal shields usually 
imbricate. Limbs and tail scaleless; two or three curved lamellee 
on the front of the forearm, and some on the hinder side of the 
leg. 
Fig. 12. 
Shell of Cinosternum leucostomum. 
Young specimens of all the species are very similar, and their 
determination meets with great difficulties. There is but a small 
difference in the size of the plastron between a newly born Cino- 
sternum of Group 1. of the following synopsis and a corresponding 
one of Group II., whilst that between the latter and one of Group IV. 
is quite insignificant, if at all perceptible. The following synopsis 
of the species applies therefore only to adult specimens. 
It must be borne in mind that, as in all Chelonians with hinged 
plastral lobes, the mobility does not exist in the quite young spe- 
cimens, and is often scarcely distinct, or restricted to the front 
lobe only, in the halfgrown. 
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