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PYGURUS 



Pygurus Michelini, Cotteau. PI. XXXV, fig. 2 a, b, c, d, e, f, g. 



Pygurus Michelini. Cotteau, Etudes sur les Echinides Foss. de l'Yonne, p. 70, 



pi. v, fig. 7, 1849. 



— pentagon A lis. Wright, Ann. and Mag. of Nat. Hist., 2d ser., vol. ix, pi. iv, fig. 



3, p. 313, 1851. 



— — Forbes, in Morris's Catalogue of British Fossils, 2d ed., p. 88, 



1854. 



Michelini. D'Orhigny, Pal. Franc, ter. Cretaces, t. vi, p. 301, 1855. 



— Davoustianus. Davoust., Note sur les Foss. specianx a la Sarthe, p. 6, 1856. 



— Michelini. Desor, Synopsis des Echinides Fossiles, p. 315, 1857. 



— — Cotteau et Triger, Echinides du departement de la Sarthe, pi. 



xiii, figs. 1 — 5, p. 65, 1858. 



Test oval, or sub-pentagonal, very slightly indented before and rostrated behind ; upper 

 surface convex, under surface concave, with prominent, cushioned, basal inter-ambulacra ; 

 apical disc nearly central ; ambulacral areas and poriferous zones widely petalloid on the 

 npper surface, contracted at the lower fifth, and lanceolate at the apex ; inter-ambulacra 

 with two flat ridges, which in each area extend from the disc to the mouth ; vent elliptical, 

 infra-marginal, lodged in a deep anal depression, with inclining sides ; mouth-opening 

 large, pentagonal, excentral ; peristome surrounded by five prominent oral lobes and five 

 depressed phylloidal fioscules. 



Dimensions. — Height, one inch and one tenth ; antero-posterior diameter, three inches 

 and one tenth; transverse diameter, three inches and one tenth. 



Description. — The first specimen of this Pygurus I obtained was an elongated subpen- 

 tagonal variety, resembling in outline some of the Yorkshire specimens, and which I erro- 

 neously referred, in my 'Memoir on the Cassidulidse of the Oolites,' to P. pentagonalis, 

 Phil. ; since that time I have collected a very fine series of this urchin, which I have care- 

 fully compared with M. Cotteau's beautiful figures, and have no hesitation in referring 

 them to Pygurus Michelini, Cott. Our English examples are larger than those from the 

 Sarthe, but in all the details of their anatomy they are identical with that form. 



The test is nearly orbicular ; in some specimens it is longer than broad, flattened, or 

 slightly concave before, and produced or rostrated behind ; the upper surface is convex, and 

 rises to a prominent vertex (fig. 2 c, d), which is sub-central, and from which the sides 

 decline unequally ; in consequence of the prominence of the single ambulacrum, the 

 posterior side forms a more regular inclined plane than the anterior side (fig. 2 d) ; the 

 border is very much undulated, and the base concave. 



The ambulacral areas are widely petalloid on the upper surface, narrow at the border 

 and base, and again expanded near the mouth ; they are sharply lanceolate at the apex, 

 and closely approximated at the disc (fig. 2 a) ; the poriferous zones on the upper surface 

 are formed of an inner row of round holes and an outer row of oblique, slit-like apertures. 



