\ 
UMM. Wilson and Crick—The Des Maristone of Tilton. 3839 
HoDIADEMA GRANULATA. 
The beautiful specimens of this Middle Lias Echinoid belong to 
a new genus, the description of which will be found in “A Revision 
of the Genera (Fossil and Recent) of the Hchinoidea,” Journ. Linn. 
Soc. vol. xxiii. 1889, by Prof. P. Martin Duncan, F.R.S., etc. The 
following is the diagnosis. 
Genus Hodiadema, Dunc. 1889. 
Test small, thin, circular in tumid marginal outline, sub-conical 
dorsally, tumid and reentering actinally, broader than high. Apical 
system moderate in size, ovoid or elliptical in outline at the peri- 
proct: five large basal plates, four in contact, but the fifth or posterior 
separated from the others on either side by radial plates, which thus 
enter the ring. Ambulacra narrow, straight, wider than the inter- 
radia at the peristomial margin, narrower elsewhere; poriferous 
zones narrow, pairs of pores numerous, in single, simple, vertical 
series, barely any crowding near the peristome; plates all low 
broad primaries; interporiferous areas rather broad, crowded with 
blunt granules dorsally, some larger granules near the poriferous 
zones, and giving place at the ambitus to some very small crenulate 
perforated tubercles, which diminish actinally. Interradia broad, 
plates not numerous, broader than high; two vertical rows of per- 
forate, crenulate and scrobiculate tubercles in each area, a few large 
at the ambitus, and all becoming rapidly small and almost obsolete 
dorsally, or replaced there by granulation, diminishing also actinally. 
Scrobicules of the ambital tubercles large, usually coalescing. A 
large blunt granulation occurs beyond the scrobicular circles, except 
on angular median spaces contiguous with the basal plates where 
there are no granules. Peristome decagonal, sunken, small, with 
well-marked branchial incisions. 
The position of this genus is in the family Diadematide and in 
the sub-family Orthopsine. 
HopIADEMA GRANULATA, sp. nov. Plate X. Figs. 5, 5a, 5b, 5c. 
Test small, sub-conical above the tumid ambitus, circular in 
ambital outline. Apical system with granulated basal plates, with 
large perforations ; the posterior radial plates large, separating the 
fifth basal plate and entering the periprocteal ring ; the others smaller, 
triangular and excluded. A raised rim around the periproct. 
Poriferous zones somewhat sunken; all plates simple primaries ; 
tubercles very small in two vertical rows. Dorsal surface of interradia, 
except in the median lines down to varying distances towards the 
ambitus, very boldly granulate; in the triangular spaces, from the 
basal plates along the median lines there is but slight granulation or 
it may be absent. About five large primary tubercles in each inter- 
radium at the ambitus, perforate, crenulate, and with coalescing 
scrobicules. Peristome reentering; with branchial incisions limited 
by raised lines. Height, 6mm.; breadth, 12mm. 
Marlstone Rock, Tilton (Hast Norton embankment). 
1 The otherwise faithful drawing, Fig. 5a, should have fewer granules upon the 
interradial plates close to the basal plates. 
