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. In a speci- 

 men before us, measuring 4^ inches in length, the mouth- 

 opening is /{jths 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 y 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 tres-renfle, convex, and 

 more elevated than in C. Tarbellianus ; but its border is a little 

 less evase, and much less tranchant. The ambulacras are equally 

 shorter, more redresses, 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, 







* M6n. sur les Ours. Foss. de Dax, p. 40. pi. 1. fig. 5-6. 



