118 Dr. T. Wright on Fossil Echinoderms 



central, and pentagonal, with five ramose ambulacral furrows, 

 sometimes branched, passing from the mouth to the border : 

 tubercles microscopically small and very numerous ; test thick, 

 interior divided by pillar-like processes: auricles five; jaws 

 forming a more or less elevated star composed of five distinct 

 pieces, each formed by the organic union of two elements ; teeth 

 five, linear, and horizontal. This genus, as now limited, con- 

 tains only fossil species, one of which is from the chalk of 

 Georgia, United States; all the others are from the tertiary 

 rocks. 



Scutella subrotunda, Leske. 



Syn. Echinus Melitensis, Scilla, De Corp. Marin, tab. 8. figs. 1-3. 



Echinodiscus subrotundus, Leske apud Klein, tab. 47. fig. 7. p. 206. 



Echinus subrotundus, Gmelin, Linne by Turton, vol. iv. p. 152. 



Scutella subrotunda, Lamarck, Animaux sans Vert. 2nd ed. tom. iii. 

 p. 284 ; Defrance, Diet. Sc. Nat. tom. xlviii. p. 230 ; Des- 

 moulins, Etudes des Echinides, no. 24. p. 232; Grateloup, 

 Ours. Foss. pi. 1. fig. 1. p. 36 ; Agassiz and Desor's Cat. rais., 

 Ann. Sc. Nat. tom. vii. p. 132. 



Test very flat, suborbicular ; dorsal surface slightly convex; 

 ambulacral areas exceeding in length the semi-diameter of the 

 disc ; base slightly concave ; mouth central ; anus marginal ; 

 ambulacral sulci bifid and branched. 



Dimensions. — Antero-posterior diameter 2y^^ inches, trans- 

 verse diameter 3y% inches, height /oths of an inch. 



Description,- — The test of this delicate Urchin is extremely 

 flat ; it has an irregular suborbicular discoidal form, with a thin 

 sinuous margin; the dorsal surface is regularly and gently 

 convex. The ambulacral areas are more than half the length of 

 the diameter of the test ; they are of an oblong form, lanceolate 

 above, and more obtuse below. The pores in the avenues are 

 widely apart ; those in the inner series are round, whilst those 

 in the external series terminate in slits that extend about half 

 way across the interporiferous spaces. The apical disc is large, 

 and the elements thereof are intimately soldered together. The 

 madreporiform tubercle occupies the centre, and the four genital 

 pores are pierced at unequal distances around it ; the anterior 

 pair are smaller and closer together than the posterior pair ; the 

 five ocular pores are very small. The margin of the disc is very 

 thin, and has a sinuous outline ; five of the curves thereof cor- 

 respond to the ambulacral areas, and those appertaining to the 

 postero-lateral areas are the deepest and best defined ; a small 

 notch indicates the site of the anal opening. The ventral surface 

 is slightly concave. The mouth, about two lines in diameter, is 

 central and subpentagonal ; from the angles thereof, five ambu- 



