from the Island of Malta. : 69 
bulacral areas. From the base of the areas to the circumference 
the margin is thin and expanded, and in this respect resembles 
a Scutella much more than a Clypeaster. The interambulacra 
between the poriferous avenues form convex elevations, which give 
a stellate character to the central dome, all the more conspicuous 
as it rises abruptly from the thin expanded margin; which is 
almost destitute of any elevation. The tubercles are larger on 
the basal than on the dorsal surface. In only one of the specimens 
before us is the inferior surface exposed. The base is flat. The 
pentagonal mouth is much smaller than in C. altus. Ina speci- 
men before us, measuring 4,7, inches in length, the mouth- 
opening is ;4,ths of an inch in diameter; the oral lobes curve 
inwards and form the interspaces thereof. Acute narrow am- 
bulacral grooves pass outwards to the circumference. 
Affinities and differences—The thin and broadly expanded 
border of C. marginatus, with its short ambulacra, and central 
dome rising suddenly from the middle of the test, form a group 
of characters which enable us readily to distinguish this species 
from its congeners, with one exception, C. Tarbellianus. The 
excellent figures of this Urchin, given by Grateloup in his able 
Memoir*, we have compared with two forms of C. marginatus 
from Malta, and we confess our inability to distinguish the 
differences between them and the author’s type-figure. Agassiz 
and Desor consider them to be the same, and we agree with their 
conclusion. 
Grateloup observes, in describing C. marginatus, “ We ought 
not to confound this species with that which I have described 
(C. Tarbellianus), with which it has great affinities of form, figure, 
and size. Its test has also a summit ¢rés-renflé, convex, and - 
more elevated than in C. Tarbellianus ; but its border is a little 
less évasé, and much less ¢ranchant. The ambulacras are equally 
shorter, more redressés, and of a more oval and acute form.” 
We have only to observe, that the characters here cited vary 
in different individuals, and at most amount to that limit of 
variation which we have already observed is seen in all species 
of Urchins, where a number of individuals of the same form are 
assembled for comparison. 
Stratigraphical range.—This species is found in bed No. 2, 
the yellow sand, associated with C. altus and the other forms 
enumerated from that stratum ; it has been found likewise in the 
Miocene beds of Touraine, Landes, Naros, Bonifacio, Santa 
Manza, Corsica; and Dax. 
History.—First figured by Scilla, and afterwards by Leske. 
Fine specimens are contained in the Mus. Jermyn Street, 
* Mém. sur les Ours. Foss. de Dax, p. 40. pl. 1. fig. 5-6. 
