BRITISH FOSSILS. 



s 



of a smaller size, in the middle, flanked by a row of secondary 

 tubercles on the inner side, and one or two rows on the outer 

 margin towards the avenues. These secondary tubercles, except 

 the outer rows, do not, in our largest specimens, reach above half 

 way up the test, and these rows, on the base, are nearly equal to 

 the primaries in size. 



The two principal rows of primary tubercles lie nearer to the 

 ambulacral rows than to each other ; they are the only ones which 

 extend all the way from the apex to the base. Their tubercles are 

 rather closely placed, and nearly of equal size throughout, wliile 

 those of the ambulacral rows are smaller towards the apex. They 

 are placed upon rather sunk mammillae, which are smooth-edged 

 above, but often present indications of the radiated muscular 

 markings on their outer margin. Each has surrounding it a circle 

 of granules of considerable size, and the entire surface of the plates 

 is covered pretty equally with similar granules, except above along 

 the median line of the interambulacra, where, for a short space, the 

 surface is bare.* 



The ambulacra are pointed above, but parallel sided below ; the 

 tubercles in two rows, about thirty-eight in a row, of which ten 

 are basal ones ; and between these, on the lower surface only, and 

 in large specimens, are four or five others of equal size, in a zig-zag 

 row. Granules surround the tubercles, and fill up the surface as in 

 the interambulacral spaces ; but here and there along the sutural 

 line the surface is smooth. The poriferous avenues are slightly 

 sunk beneath the general surface, especially near the mouth. Their 

 breadth above is about half that of the rest of the ambulacral space, 

 — a little less at the turn of the margin, and then again it widens 

 out considerably. The pores are ranked in threes, in parallel and 

 but slightly oblique rows in this variety (with a row of about three 

 granules between each set), except near the apex, where the ranks 

 are much more oblique. Each pair of pores is surrounded by an oval 

 ring, and set obliquely, but not so much so as in our figure. There 

 is no tubercle or bar between the pores. The mouth is pentagonal, 

 with two deeply incised* notches at each angle beneath the inter- 

 ambulacral spaces. Between these the oral margin is rounded, but 

 beneath the ambulacra it is nearly a straight line. The apical disk 

 is well preserved ; we have figured it from both varieties ; the 

 round variety (fig. 6), in which the ovarian plates are somewhat 

 more obtuse, and the var. germinans. In the latter the five genital 



* This character exists to a much gTeater extent in the alosely allied E. gyrains, Ag. 



