400 PYGURUS 



Pygurus Blumenbachii, Koch and Bunker. PL XXXVIII, figs. 1 and 2. 



Cltpeaster Blumenbachii. Koch and Dunker, Norddeutschen Oolithgebildes, pi. iv, 



fig. a, h, c, p. 37, 1837. 

 Pygurus Blumenbachii. Agassiz and Desor, Catalog, raisonne des Echinides, Annales 



des Sciences Naturelles, 3' serie, t. vii, p. 162, 1847. 



— — D'Orbigny, Prodrome de Paleont. Stratigr., t. i, p. 26, etage 



14% 1850. 



— ' — Wright, Ann. and Mag. of Nat. Hist., 2d series, vol. ix, 



p. 312, 1851. 



— — Forbes,iuMorris'sCatalog.ofBrit.Fossils,2ded.,p.88,1854. 



— — Cotteau, Etudes sur lesEchinides Fossiles (Yonne), pis. xxxiii 



and xxxvi, p. 233, 1856. 



— — Desor, Synopsis des Echinides Fossiles, p. 313, 1858. 



Test thin, sub-quadrate, with a sinuous border ; upper surface elevated anteriorly, 

 gradually declining posteriorly; apical disc excentral forwards, forming the vertex; 

 ambulacral areas and poriferous zones broadly petaloid on two thirds of the dorsal 

 surface ; anterior border emarginate and concave ; sides crescentic ; posterior border 

 produced, rostrated, and much deflected ; under surface concave, with prominent basal 

 inter-ambulacra. Mouth-opening large, sub-central ; peristome with five very prominent 

 oral lobes, and five phylloid ambulacral floscules. Tubercles in general small, but larger 

 on the anterior part and at the base. 



Dimensions. — Height, one inch and a quarter ; antero-posterior diameter, two inches 

 and one fifth; transverse diameter, two inches and three tenths. 



Description. — The Oolitic Pyguri, in general, have a remarkable similarity in their 

 external form ; so much so, that it frequently requires a careful examination of their 

 characters to distinguish allied species from each other. It is, however, altogether 

 different with Pygurus Blumenbachii, which forms a remarkable exception to the general 

 rule. In this singular urchin the outline is sub-quadrate, the anterior border is emargi- 

 nate and concave, and deeply indented by the central sulcus (fig. 1 a, fig. 2 a) ; the lateral 

 parts of the margin are convex ; the posterior border consists of a double sinuous line, in 

 the centre of which is the single inter-ambulacrum, this forms a convex, rostrated pro- 

 minence, slightly defiected downwards (fig. 1 a, fig. 2 a). The upper surface presents a 

 most singular profile (fig. \ d) ; the anterior half is relatively much elevated and turgid, 

 and the posterior half slopes gently downwards to the border. 



The dorsal ambulacra are broadly petaloid at the upper half and extremely narrow at 

 the lower half, and their wide, lanceolate apices are closely approximated around the disc 

 (fig. 1 a, fig. 2 a). 



The poriferous zones consist of an inner row of round holes and an outer row of 



