214 THE FOSSIL ECHINOIDEA 



length ; the abactinal surface is convex and regularly arched from the apex to the 

 thin angular margins. Seen in longitudinal profile the anterior slope, which passes 

 through the apical disk, is rather less full and less rapid than the posterior slope, and 

 when seen in transverse profile the slightly prominent carination of the odd posterior 

 interradium is noticeable. On the actinal surface there is a very marked declivity or 

 inclination of the test around the peristome, especially anteriorly, which gives a remark- 

 able appearance to the species. 



The apical disk is slightly excentric in front ; the two anterior generative pores are 

 rather wide apart and separated by the odd anterior ocular plate ; the posterior pair of 

 generative pores are rather wider apart than the anterior pair ; and the posterior pair 

 of ocular pores are separated by the central madreporiform body. The ocular pores are 

 minute and almost microscopic. 



The odd anterior ambulacrum lies in a very slight depression of the test, which 

 can scarcely be called a groove, and the grooves of the petaloid ambulacra are almost 

 as shallow and ill-defined ; these latter appearing, however, to be rendered visible by 

 the slight tumidity, verging on carination, which occurs along the median line of the 

 interradia. 



The anterior pair of petals are a little longer than the posterior pair, haying two 

 or three more pairs of pores in each zone; they are very widely divergent, sub- 

 tending an angle of about 160°, and the general course of the petal is almost straight 

 from the apex towards the margin, although a certain appearance of curvature is pro- 

 duced by the rapid abortion of the seven or eight terminal pairs of pores at the apical 

 extremity of the anterior zones. The pores in each zone are equal, transversely oval, 

 and wide apart ; the pores of a pair are united by a conjugating furrow, and adjacent 

 pairs separated by divisional costse, and the width of the interporiferous area is about 

 equal to the distance of the pores apart. In the posterior petals two or three pairs of 

 pores are aborted in each zone at the apical extremity, and the succeeding pores are 

 smaller, increasing in size more gradually in the posterior zone than in the anterior 

 zone, producing the appearance of more extended abortion ; but the character is much 

 less conspicuous than in the anterior zones of the anterior pair of petals. The posterior 

 pair of petals subtend an angle of about 40°. 



The peristome is excentric in front and situated in a well-defined and rather deep 

 depression of the test ; the anterior lip is semicircular ; the posterior lip is unfortunately 

 destroyed. The five or six terminal pores of each ambulacral zone near the peristome 

 are large and situated in cavities, and form in each ambulacrum a pair of uniserial 

 lines of pores, which diverge apart as they approach the peristome. 



The position and character of the periproct is undeterminable, as the upper part of 

 the posterior extremity is wanting. 



The posterior peak of the actinal plastron is rather prominent, and the longitudinal 

 diameter of the subanal plastron appears to have been small, probably about one fourth 

 of the transverse diameter. About four pairs of ambulacral pores are present on either 

 side of this plastron, although no trace of the subanal fasciole, whose presence is thus 

 demonstrated, can be made out. 



