48 BRITISH FOSSIL REPTILES. 



the neural plate. The second costal plate, on the contrary, is broader at its lateral 

 than at its mesial end in Tri. Henrici, whilst its breadth is equal at both ends in the 

 figure given by Cuvier of the Tri. Maunoir. The thickness of the costal plates, in 

 proportion to their breadth, may be known by reference to PI. 31, figs. 4 and 5 ; 

 and the degree of projection of the connate rib from the inner surface of the costal 

 plate by figure 6 ; the Tri. Henrici closely agreeing with Tri. marrjinatm in these 

 respects. The peripheral border of the carapace is not grooved in this species, as in 

 the Tri. circumsulcatus, fig. 3. 



The degree of transverse convexity of the carapace of the Tri. Henrici is the same 

 as that of the Tri. JEr/i/piiacus, and as that attributed to the Tri. Maunoir.* 



The nuchal plate is wanting in Lady Hastings's specimen ; the one which is 

 figured in PL 6, fig. 3, is from the same locality at Hordvvell, but does not belong to 

 the carapace, fig. 1, although it has probably belonged to one of the same species, 

 from the contour of its hinder border. 



The first neural plate {s\) does not project beyond the adjoining anterior borders 

 of the first costal plates {jih) as it does in Tri. subplanus, Tri.ferox, and Tri. javanicus ; 

 nor do those borders, as they recede from the neural plate, curve forwards beyond it, 

 as in Tri. javanicus\ and Tri. coromandelicus.\ 



The anterior border of Tri. Henrici is slightly concave and gently undulated, as 

 in the Tri. jE(/yptiacus, and is also rough and sutural, showing that the anterior azygos 

 or nuchal plate ("piece impaire," Cuv.) had been immediately articulated with it, as 

 it is in Tri. ^(jyptiacus.% 



The fossil specimen of the nuchal plate, figured in PI. 6, fig. 3, shows, by the 

 sutural structure of its posterior border, that it articulated with the anterior sutural 

 border of the carapace to which it belonged, and which, as already remarked, belonged 

 probably to the species Tri. Henrici, though not to the individual the carapace of 

 which is figured in PI. 6, fig. 1. 



The neural plate («i) is longer in proportion to its breadth, and the corresponding 

 costal plates {ph) are narrower at their extremities than in Tri. JEgy2)tiacm. The 

 second costal plates («2) are broader at their extremities than in Tri. JEgyptiacus ; 

 they resemble those in Tri. suhi)laniis.\ 



The first four neural plates in Tri. Henrici slightly expand posteriorly, and have 

 their posterior angles cut off; the fifth («5) is a narrow plate with entire angles ; the 

 sixth (m6) is expanded anteriorly, and has its anterior angles cut off ; the seventh (»") 

 has also its anterior angles cut ofi^, but is rounded behind, and, as it were, obliterated 



* " Sa conve.\ite transversale est telle, que la fleche de Tare est moindre du cinquieine de la corde." 

 (Cuvier, Ossemens Fossiles, torn, v, pt. 2, p. 223.) 

 f Annales du Museum, torn, .xiv, pi. 3, A. 

 X Ibid., pi. 5, fig. 1. 

 § Ibid., pi. 2, A, a. 

 II Ibid., pi. 5, fig. 2. 



