114 Dr. T. Wright on Fossil Echinoderms 



surface of C. umbrella, with its flattened ambulacral areas and 

 convex prominent interambulacral spaces, its star-like apical 

 disc and small mouth-opening, widely distinguish this species 

 from C. alius. The affinity, however, is very near between 

 C. alius and C. crassicosiaius, the principal difference consisting 

 in the more prominent rib-like prominence of the ambulacral 

 areas. 



Siraiigraphical posiiion. — This is the most abundant of all 

 the Maltese Urchins. It is collected from bed No. 2, the 

 yellow sand, associated with C. Tarbellianus, Echinolampas 

 Richardi, and the other Echinoderms enumerated in the palseon- 

 tological resume given in the introduction to this memoir. The 

 test is very well preserved in most specimens. Those from the 

 sand with black particles are in the finest preservation. In this 

 stratum the Urchins are accompanied with Terebratula ampulla, 

 Pecien squamulosus, P.Burdigalensis, Ostrea Virleii,0. navicularis, 

 and masses of Leniiculiies complanatus, with Cellepora mammil- 

 lata, Escharina monilifera, and other Bryozoa. 



It has been collected from the Miocene beds of Port-de-Bouc, 

 Saint-Miniato, Tuscany; Nice, Turin, He de Crete, He de 

 Capree; Bonifacio, Corsica; Oran. The Maltese specimens are 

 contained in the British Museum, Geological Museum, Jermyn 

 Street, and Bristol Museum ; that from the He de Capree is in 

 our cabinet. 



History. — First figured by Scilla, in 1670. The list of 

 synonyms prefixed to this article exhibits the various epochs in 

 its history. In none of the works we have consulted is any 

 detailed description of the species given. 



Clypeaster marginaius. Lam. 



Syn. Scilla, Corp. Mar. tab. 1 1 . fig. inferior. 



Clypeaster marginatus, Lam. An. sans Vert. torn. iii. p. 290, 2nd 

 ed. ; Deslongchamps, Encycl. Method, t. ii. p. 200 ; Defrance, 

 Diet. Sc. Nat. t. ix. p. 450; Blainville, Man. Act. p. 216; 

 Grateloup, Foss. Ours. p. 40; Agassiz and Desor, Cat. raisonne, 

 t. vii. p. 131 ; Desmoulins, Etudes des Echinides, no. 12. p. 218. 



Test large, depressed, subpentagonal ; margin thin, broad, and 

 expanded ; outline of the border undulated ; ambulacral areas 

 short, oval, and convex, rising abruptly from the thin border, 

 and forming a dome-shaped elevation in the centre of the 

 dorsal surface; base flat; mouth-opening small and penta- 

 gonal, with five simple sulci extending from the angles 

 thereof to the margin ; anus small, round, and submarginal. 



Dimensions. — Antero-posterior diameter 6^^^ inches, breadth 

 Q-^-Q inches, height at the centre \^j^ inch, thickness of the 

 margin about ^th of an inch. 



