Srom the Lias and Oolites. 27 
stinct and devoid of details, that it is impossible to institute a 
strict comparison between our Urchin and the one figured by 
him. The difference between D. Davidsoni and D. subangulare 
is so marked that it is impossible to mistake them—the penta- 
gonal outline, large tubercles, wide granulated space between 
the primary tubercles of both areas, with the pores arranged in 
double files on the upper surface of the test, form a group of 
characters which distinguish D. subangulare from our Urchin. 
From D. pseudodiadema it is distinguished by the tubercles in 
D. Davidsoni of the ambulacral equalling in size those of the 
interambulacral areas, whilst in that species they are unequal. 
The rudimentary condition of the secondary tubercles in our 
species forms a striking contrast to the size they attain in 
D. pseudodiadema. The naked condition of the central parts of 
the interambulacral areas connects it with D. subnudum, Ag., of 
the Chalk, and the neatness of its outline allies it with other cre- 
taceous forms. 
Locality and stratigraphical.range-—We have collected this 
species in the clays of the Coral rag near Calne, Wilts; it is a 
very rare Urchin, as we only know four specimens of it. 
We dedicate this species to our friend Thomas Davidson, Esq., 
whose learned monographs on the Brachiopoda have earned him 
the gratitude of all paleontologists. We take this opportunity 
likewise of recording our deep obligations to Mr. Davidson for 
many friendly acts of assistance given during the preparation of 
these memoirs, by which we have been enabled to compare a con- 
siderable number of foreign Echimide with those of our own 
island, and thereby have been enabled to obtain a better know- 
ledge of the affinities existing among the Echinoderms of the 
European Oolitic fauna. 
Diadema Moorei, Wright. PI. II. fig. 3, a—d. 
Test circular, depressed ; ambulacral tubercles smaller than those 
of the interambulacral areas ; plates of the test covered with a 
small wide-set prominent granulation ; mouth large and deca- 
gonal; anal opening large ; apical disc of moderate size. 
Height ,°,ths of an inch, transverse diameter 42ths of an inch. 
Description.—There is much difficulty in distinguishing some 
of the smaller Diademas from each other, inasmuch as the young 
condition of many of the larger species so closely resembles the 
adult state of others, that it is only after one obtains a number 
of individuals of different species in their various phases of 
growth, that the naturalist feels himself upon sure ground when 
he endeavours to distinguish the affinities and differences that 
exist among them. ~ 
