312 THE FOSSIL ECHINOIDEA 



third is between the median and the innermost vertical series of pores. The vertical 

 rows are maintained with great regularity, but there is considerable irregularity in the 

 respective posture of the tubercles of the two rows between the outer and the median 

 series of pores. Frequently two of these tubercles stand in horizontal line, and are 

 well spaced from the next pair, but frequently the tubercle of one vertical row is not in 

 horizontal line with the corresponding tubercle of the other. The tubercles which 

 stand between the median and the inner vertical series of pores appear to be placed 

 regularly opposite the interspaces between the tubercles of the innermost of the two 

 vertical series of tubercles which occupy the space between the outer and the median 

 series of pores, and are also in horizontal line with the nearest tubercle on the inter- 

 poriferous area. In addition to these primary tubercles a few small miliary (but still 

 mammillated) tubercles occur irregularly upon the ambulacral plates. There are five 

 ambulacral plates opposite one of the interradial plates at the ambitus, and consequently 

 five of the pairs of pores belonging to the outer vertical series. 



The interradial plates are broad but short, their breadth at the ambitus being 

 more than five times the length, the actual dimensions being 25 millim. and 4*5 millim. 

 respectively. Each plate bears a horizontal line of uniform and equal-spaced primary 

 tubercles, slightly larger than those on the ambulacral areas. In the neighbourhood 

 of the ambitus there are seven tubercles in this horizontal line, the position of which 

 upon the plate is rather below the middle. At the end of the plate adjacent to the 

 poriferous zone an additional primary tubercle of equal size to those described stands 

 near the aboral margin of the plate, immediately over the interspace between the two 

 first tubercles of the horizontal line, there being thus eight primary tubercles on each 

 plate at the ambitus ; as the plates recede from the ambitus, however, the tubercles of 

 the horizontal series nearest the poriferous zone diminish to the size of mere secondary 

 tubercles, or disappear altogether, which causes the horizontal line of tubercles to 

 appear to take a sharp angular bend at the extremity near the poriferous zone. Some- 

 times in the larger plates near the ambitus there is a small secondary tubercle in the 

 extreme aboral corner of the plate, close to the poriferous zone ; and an irregular line 

 of mammillated miliary tubercles stands on the aboral margin, whilst a few irregularly 

 disposed and very much smaller simple miliary granules are distributed on the vacant 

 portions of the plate. 



Unfortunately neither the peristomial nor the apical regions of the test are 

 preserved. 



Bemarks. We refer to this species, although with some doubt, a fragment, con- 

 sisting of part of an interradial and an ambulacral area. It belonged to a much smaller 

 test than the type-specimen above described. The interradial plates at the ambitus 

 bear a horizontal row of five primary tubercles and a distinct line of miliary tubercles 

 along the aboral margin, the one nearest the poriferous zone being the largest of these. 

 The tubercles are more numerous and much more closely placed than in considerably 

 larger examples of the allied species H. antiqm, described below ; and on these grounds 

 we consider it probable that the fragment belonged to a young test of E. proavia. The 

 fragment in question is figured in Plate XLIX. 



