206—52 INDIAN TERTIARY AND POST-TERTIARY VERTEBRATA. 
figured in the accompanying woodcut, which was obtained by Mr. Blanford from the 
lower Siwaliks of Sind. 
Trionyx, sp. The greater part of the fii-st left costal scute ; from the 
lower Siwaliks of Sind. Indian Museum (No. E 129). y 
The specimen comprises the greater part of the first left costal scute, perfect 
distally, but wanting a small portion at its vertebral extremity and on its hinder 
border. The anterior border is formed by the first rib, which presents an anterior 
and a superior surface, both of which have no trace of sculpture. The anterior 
surface is a free one, and shows that the nuchal scute did not unite by suture with 
the 1st costal. That portion of the scute situated posteriorly to the rib is covered 
with a well-marked sculpture, consisting of conical tubercles, and quite different 
in structure from that of the last species or Chitra. 
Nuchal scute. — A fragment of the scute of a Trionyx from the Siwaliks of the 
Punjab in the Indian Museum (No. E 130) agrees in the character of the sculpture 
with the preceding specimen. Owing to its imperfect condition it is somewhat 
difficult to be quite sure of the position it originally occupied in the shell, but it 
appears to be a portion of the left half of the nuclial scute, and indicates an 
individual fully as large as the last specimen. It is entirely rugose, and both the 
anterior and posterior borders are free, and the under surface is bevelled away in 
front of the latter. It cannot be certainly determined whether this specimen belongs 
to the same species as the last, although this may well have been the case ; but in 
either case it indicates a -form with a nuchal scute not suturally connected with the 
1st costal. 
Distinctness and affinities . — The structure of the present specimens at once shows 
that they indicate a form allied to the group referred to on page 203, in some of 
which the nuchal scute is not suturally connected with the 1st costal, and is frequently 
imperfectly sculptured. None of the recent forms, however, appear to have the 
anterior half of the 1st costal unsculptured, as it is in the fossil. The nature of the 
sculpture of the latter agrees very closely with that of T. guentheri^ and is quite 
different from that of T. ornatus^ ; the fossil nuchal scute agrees moreover with the 
former in being completely sculptured, and thereby differs from the latter, in the 
1 lldc Giinthcr, “ Keptiles of British India,” pi. VI. fig. A. 2 Ibid, fig. B. 
