102 Dr. T. Wright on Fossil Echinoderms 



with an imbricated arrangement on the plates, on each of which 

 a perforated tubercle is raised. The basal portions of the inter- 

 ambulacral pairs are covered with wider-set tubercles of the same 

 size, and the entire upper surface of the test is crowded with small 

 tubercles closely set together, and very uniform in size and 

 arrangement. The mouth is surrounded by five petaloid pori- 

 ferous ambulacra. 



Affinities and differences. The excentrical position of the disc, 

 with its four genital holes, and the petaloid poriferous ambulacra 

 around the mouth, establish an affinity between this form and 

 Srissus. The way in which the peripetal joins the marginal 

 fasciole is similar to what exists in Schizaster, whilst the mar- 

 ginal fascicle, entirely encircling the test and passing round 

 beneath the anus, is found only in Pericosmus. The excentral 

 position of the apical disc and the shallowness of the am- 

 bulacral star form a sufficient diagnosis between this species and 

 P. latus. 



Locality and stratigraphical position. Collected from bed 

 No. 1, the Gozo marble at Malta, where it is rare. 



Genus SCHIZASTER (Agassiz, 1834). 



Urchins with a cordiform test, broad and depressed before, 

 narrow and elevated behind ; the ambulacral summit excentral 

 and nearer the posterior border ; the petaloid ambulacra lodged 

 in very deep depressions, the antero-lateral much longer than 

 the postero-lateral pair; the single ambulacrum long and deeply 

 sunken in the anteal sulcus; the peripetal fasciole surrounds 

 the ambulacral star, and from one of the antero-lateral angles 

 thereof, a second postero-lateral fasciole arises, which passes 

 downwards and backwards along the sides and under the anus, 

 where it joins its fellow of the opposite side ; the genital pores 

 are two in number from the fusion of the anterior and posterior 

 pairs ; the five ocular plates are small and lodged in depressions ; 

 the eye-holes are microscopic. Schizaster differs from Hemiaster 

 in possessing a postero-lateral fasciole, and in having the antero- 

 lateral ambulacra less divergent and lodged in deeper depressions ; 

 the anteal sulcus is also much deeper. 



Schizaster eurynotus, Agassiz. 



SYN. Echinus Spatangus compressus et lapidescens in Melitensi 



topho, Scilla, Corp. Mar. tab. 7. fig. 1. 

 Echinus gladiatus vestitus et nudus Imperati, Klein, Echinod. p. 35. 



tab. 27 A. 



Spatangus lacunosus, Leske, no. 77. p. 227. 

 Spatangus canaliferus, Lamarck, Anim. sans Vert. 2nd ed. torn. iii. 



p. 327; Grateloup, Foss. Ours. Dax, p. 67. 



