70 Dr. T. Wright on Fossil Echinoderms 
British Museum, Bristol Museum, and the Collection of the 
Earl Ducie. The specimen in our cabinet is from Santa Manza, 
and was sent us by M. Michelin. 
Clypeaster folium, Agassiz. 
Syn. Clypeaster folium, Agassiz and Desor’s Cat. rais., Ann. Sc. Nat. 
tom. vil. p. 131. 
Test subheptagonal, much depressed; borders thin and sharp 
like Scutella; the petaloid ambulacra short, open, and ex- 
panded below ; acutely lanceolate at the apex; ambulacral 
rosette small, and rising gently from the middle of the dor- 
sum ; poriferous zones lie in angular depressions ; apical disc 
small, with a central prominent madreporiform tubercle. 
Dimensions.—Antero-posterior diameter 137 inch, transverse 
diameter 134 inch, height ,3,ths of an inch. 
Description.—The general outline of this little Urchin, with 
the structure of its ambulacral rosette, clearly prove it to be a 
Clypeaster, whilst its depressed dorsal surface and thin border 
show it to have affinities with Scutel/a. Its outline is subhep- 
tagonal, with the anterior border slightly produced ; the petaloid 
ambulacral areas are short and widely expanded below, tapering 
and acutely lanceolate above; their apices closely approach at 
the vertex, and meet at the circumference of the madreporiform 
tubercle; the poriferous zones lie in angular depressions of the 
test, which, added to the convexity of the ambulacra, give a 
much greater relief to the petaloidal star than in other congeneric 
forms ; the rosette formed by the petaloid portions of the ambu- 
- Jacra is small, being only a little more than one-half the diameter 
of the antero-posterior axis. The two rows of pores in the pori- 
ferous zones diverge gently from each other from the apex to the 
base, and there are from thirty to thirty-six pairs of holes in 
each zone. At the junction of the test-plates there are slight 
depressions on the surface, corresponding to the sutures between 
the same ; the tubercles are small and set rather closely together, 
and the intervening granulation is quite microscopic ; the border 
is exceedingly thin and entire; the base is concealed by firmly 
adherent matrix, which cannot be removed without fracturing 
the test. 
Affinities and differences.—C. folium is allied to the young 
condition of C. marginatus, but the general flatness of the dorsal 
surface, and the absence of the campanulate elevation of the 
ambulacra in that species, added to the greater wideness of the 
basal opening of the petaloid ambulacral areas, and the more 
angular depression in the poriferous zones, afford points of 
comparison whereby these two species may be distinguished 
