114 THE FOSSIL ECHINOIDEA 



situated nearer the adoral margin of the plate ; the arrangement of the tubercles is 

 consequently slightly oblique upon the plate. 



The interambulacral a,reas are twice and a half the breadth of the ambulacra at 

 their widest part — the ambulacra being 8 millim., the interambulacra 20 millim. There 

 are two rows of about 12 primary tubercles in each interambulacrum (possibly 13, 

 but the number cannot be stated definitely on account of the concealment of the 

 abactinal area by matrix). The primary tubercles are of moderate height, the neck 

 broad and deeply crenulated (about a dozen being present), and the mamelon very small, 

 subangular at the margins, and perforate. The scrobicules are wide and transversely 

 oval*. The scrobicular circle is subcomplete, and more or less confluent adorally and 

 ah orally, composed of 19 or 20 small, mammillated, miliary granules, scarcely larger 

 than the rest of the granulation of the plate. The miliaries are uniformly and rather 

 widely spaced and all are mammillated. The space between the scrobicular ring and 

 the poriferous zone has about two alternating series of miliaries external to those of 

 the ring; the space between the median suture of the area and the scrobicular ring is 

 more than twice as broad, and contains, in addition to three or four alternating series 

 of miliaries external to the scrobicule, a number of granules which gradually diminish 

 in size as they recede from the scrobicular ring. This gives the miliary zone a some- 

 what naked appearance. In some plates a faint indication of delicate furrows running 

 from the miliary zone outwards towards the scrobicule may be made out, inclosing 

 single series of granules ; but this is by no means persistent, and the furrows seldom 

 extend the whole way. 



In primary tubercles where the preservation is perfect, shallow radiating grooves 

 or flutings may be traced at the base of the boss, deepest at the very margin of the 

 scrobicule, about 16 to 20 in number all round, although their presence is very' 

 indistinct adorally and aborally. The character is very feebly marked throughout, and 

 where weathering influences have taken place is altogether undiscernible. 



Peristome decagonal or subpentagonal, small, 15 millim. in diameter in a test 

 49 millim. in diameter at the ambitus. Interambulacral plates prominent, with margin 

 incurved at the median suture and rounded towards the poriferous zones, simulating an 

 actinostomial indentation. Apical disk unknown. 



Eadioles. The weathered longitudinal section of a primary radicle is present 

 amongst the matrix on the abactinal area, and also several fragments. This spine is 

 of moderate breadth and very slightly expanded as it increases in length. At each side 

 occur uniform, widely and equidistantly placed serrations, and the shaft is probably 

 compressed. The articulating facet is small in correspondence with the small mamelon. 

 The head is short and expands very rapidly, the ring prominent. The shaft contracts 

 gradually a short way outward from the ring, and again expands up to about the 

 second serration ; outward beyond this the expansion is very slightly, if at all, continued. 



Numerous miliary spinelets are preserved upon the test; they are elongate, 

 delicate, compressed, slightly tapering and rounded at the extremity, all uniformly 



* This character has unfortunately not been sufficiently shown by our artist in his drawings of this 

 species. 



