ME J. W. GREGORY ON THE MALTESE FOSSIL ECHINOIDEA. 



613 



Professor Loven has pointed out that the Echinoids that inhabit deep water have 

 their petals less impressed than those that live in shallower seas. If this character can 

 be relied on, then the zones on which this species occurs may mark periods of especial 

 depression in the Maltese area. The species may, in fact, be the deep-sea representative 

 or variety of H. scillae. Apart from the other varieties, the difference in the petals 

 seems quite of specific value. The species, however, helps to throw doubt on the 

 advisability of classifying the Spatangoids into those with flush petals (Spatangidse), and 

 those with depressed petals (Brissidse), as is at present done by some eminent foreign 

 Echinologists. A character that may be independently acquired at any time by a mere 

 migration to deeper water is not one that can be adopted as a family character.* 



This species agrees more closely with Hemiaster gibbosus, A. Ag.,t than with any 

 fossil species that I know. It differs from this deep-sea form in that this has the 

 posterior margin more vertical, and the maximum width at the posterior end (see Pro- 

 fessor A. Agassiz's figure, No. 6). As the apical disc is ethmophract, it belongs to 

 Hemiaster even as limited by M. Pomel. 



Genus Pericosmus, Agassiz, 1847. 



Species 1. Pericosmus latus (Agassiz), 1840. 

 Synonymy — 



Micraster latus, L. Agassiz, 1840, Cat. Syst. Ectyp. Foss. Mus. Neoc, p. 2. 



Pericosmus {Hemiaster) latus, Agassiz and Desor, 1847, Gat. rais. Ann. Set. Nat. Zool. (3), t. viii. 



p. 19 ; t. vi. pi. xvi. f. 1. 

 T. Wright, 1855, "Foss. Echinod. Malta," Ann. Mag. Nat. Hist. (2), 



xv. pp. 193-5. 

 E. Desor, 1858, Syn. Ech. foss., p. 396. 

 ,, K. Mayer, 1864, in Hartung Oeol. Beschreib. Madeira und Porto Santo, 



p. 193. 

 ,, T.Wright, 1864, "Foss. Echinidse Malta," Quart. Journ. Oeol. Soc, 



xx. p. 4S7. 

 „ A. Locard, 1873, " Faune terr. tert. Corse," Bull. Soc. geol. France 



(3), i. p. 238. 

 „ A. Manzoni, 1873, "II Monte Titano," Boll. E. Com. geol. Italia, 



iv. p. 20. 

 „ G. Cotteau, 1877, " Faune terr. Corse," Ann. Soc. Agric. Lyons (4), 



ix. pp. 316-318. 

 „ A. Manzoni, 1880, "Ech. foss. Mol. Serp.," Derik. Ale. Wiss. Wien, 



xlii., abt. ii., p. 187, pi. ii. f. 16, 17. 

 „ G. Mazzetti, 1882, "Ech. foss. Montese," Atti Soc. Nat. Modena (2), 



xv. p. 115. 



* S. Loven, " On Pourtalesia, a Genus of Echinoidea," Kongl. Svensk Vetensk. Ah. Handl., N.s., xix., No. 7, 

 1883, p. 95. 



f Al. Agassiz, " Preliminary Eeport on the Echini of the Exploring Expedition of H.M.S. ' Challenger,' " Proc. 

 Amer. Acad. (Boston, 1879), xiv. p. 210. Al. Agassiz, " Eeport on the Echinoidea dredged by H.M.S. ' Challenger ' 

 during the years 1873-1876," Challenger Reports, Zool. III., No. 1, 1881, pp. 184-186, pi. xx. f. 5-16. 



