184 THE FOSSIL ECHINOIDEA 



Genus EHYNCHOPYGUS, d'OrUgny, 1801. 



(See cvniea, p. 67, Part ii.) 



1. Rhtnchoptgus Caldbei, d'Archiac & Haime, sp. Plate XXXIII, Figs. 1-6. 



Eurhodia Calderi, d'Archiac 8f Haime, Descrip. Anim. foss. du groupe numm. de I'Inde, p. 352, pi. xxx, 

 fig. 19. 



Test of moderate size. Marginal contour suboval, rather flattened at the sides, 

 somewhat elliptically rounded in front, and distinctly truncate posteriorly, where it is 

 also slightly reenteringly curved. In some examples the greatest width is in a line with 

 the extremities of the postero-lateral petals ; and a somewhat angular protuberance is 

 produced in the contour by the rather rapid rounding of the margin from this point 

 until it joins the posterior truncation. The breadth is usually about three fourths of the 

 length ; but in some cases the disproportion is slightly less. The dorsal surface is 

 moderately high, with a subcarinate or rounded ridge along the longitudinal axis, from 

 which the sides are inclined roof-like. The vertical height at the summit is rather more 

 than one half the length. The apical summit of the test is excentric in front ; and when 

 seen in longitudinal profile the dorsal surface shows a more rapid anterior than posterior 

 slope, the disparity, however, being variable and dependent on the greater or less 

 «xcentricity of the summit. 



The transverse profile exhibits an arch-like contour, produced by the longitudinal 

 earination of the test. The margin is tumid, but less so posteriorly, and more or less 

 conspicuous protuberances are present at the posterior third and near to the posterior 

 truncation. When seen in profile, the ambitus presents a graceful curve, in consequence 

 of the anterior part of the test being on a slightly higher level than the sides ; and there 

 is a corresponding upward slope posteriorly, starting from the protuberance on the 

 margin, which stands in line with the extremities of the postero-lateral petals. The 

 anterior portion of the dorsal surface is rather more sharply carinate than the posterior 

 portion, which is frequently more rounded. The longitudinal keel is terminated 

 posteriorly by a prominent lip, which overhangs the periproct. The actinal surface is 

 concave, a more or less distinct longitudinal trough being frequently produced. 



The apical disk is small and inconspicuous, usually a little in advance of the summit 

 of the test. The four small genital plates have moderately large pores, which are 

 almost equidistantly spaced. The ocular plates are very minute ; those in connexion 

 with the odd and the anterior pair of petals lie between and separate their neighbouring 

 genital plates ; whilst those in connexion with the posterior pair of petals are placed on 

 the inner side of the posterior genital plates, and are separated from one another by an 

 extension of the madreporiform body, which also occupies the whole of the central 

 portion of the disk. 



The ambulacral petals are flush with the surface of the test and unequal. The odd 

 anterior ambulacrum is large, broad, open anteriorly, and has broad poriferous zones ; 

 the line of the inner pores is nearly straight, and that of the outer pores forms a curve. 



