258 PYGURUS. 



narrow, perforated, and a single rudimentary imperforate, ovarial plate ; five minute 

 ocular plates, are interposed between the ovarials (PI. LVIII, fig. 1 h). 



The small madreporiform body is attached to the surface of the right anterior ovarial, 

 and forms thereon a spongy eminence, which extends over the other discal elements. 



The tubercles are very small on the upper surface, and larger at the base ; they are 

 surrounded by sunken areolas, and have their summits perforated ; the intertubercular 

 space is covered with close-set miliary granules (PI. LVIII, fig. 1 ^). 



The genus Fygurus first appears in the Lower Oolites, and its species are likewise 

 found in the Inferior Oolite, Puller's Earth, Great Oolite, Cornbrash, Kelloway Rock, 

 Coralline, and Portland Oolite. 



In the Cretaceous formations the species Fi/(/urus rostraius, P. GiUieroni, P. 

 Buchii, characterise the Lower Neocomian or Valangian ; Pygurus Monfmolini and P. 

 Salevcnsis are found in the Middle Neocomian ; Pygurus productus comes from the 

 Urgonian ; Pygurus Eicordeanus from the Gault ; Pygurus Lampas from the Upper 

 Greensand or Cenomanian. Of the eight Cretaceous species one is found in the English 

 Upper Greensand, where it is so rare that I know only of two specimens, and one of 

 these is preserved in the British Museum. 



Pygurus Lampas, Be la Beche, 1819, PI. LVIII, figs. \a — \h. 



Clypeaster oviformis, Lamarck. Anim. sans Vert^bres, t. iii, p. 15, 1816. 

 EcHiNOLAMPAs Lampas, De la Beche. Geol. Trans., 2nd eer., p. 112, t. iii, fig. 3, 1819. 

 Pygduus trilobus, Agassiz. Cat. Syst. Ecty., p. 5, 1840. 



— — Jffassh and Desor. Cat. rais., p. 103, Modele No. 39, 1847. 



— — d'Orbigny. Prodrome, t. ii, p. 178, Etage 20, 1847. 



— OVIFORMIS, d'Orbigny. Pal. Fran9aise, t. 91 9, torn, vii, p. 311, 1855. 



— Lampas, Desor. Synopsis Echinides foss., p. 311, 1858. 



Biagnosis. — Test high, very convex above and concave beneath, much longer than 

 wide, largely rostrated, and abruptly truncated behind ; ambulacra lanceolate, poriferous 

 zones subpetaloidal, apical disc and vertex excentral ; base very concave and much undu- 

 lated ; mouth excentral ; peristome surrounded by a pentapetaloid floscelle of complicated 

 structure ; interambulacrum much developed, recurved, and truncated ; vent transverse 

 and infra-marginal. 



Bimensions. — This very I'are British Urchin was first noticed by my old esteemed friend 

 Sir Henry De la Beche, E.R.S., who collected it from the Upper Greensand near Lyme 

 Regis, and figured it in the ' Transactions of the Geological Society,' depositing the specimen 



