NO. 3 CASSIDULOID ECHINOIDS — KIER 47 



Apical system. — Anterior, tetrabasal, with four genital pores. 



Ambulacra. — Petals broad, equal, long, extending over two-thirds 

 distance to margin, closed, with very wide interporiferous zones, 

 strongly tapering distally. Poriferous zones narrow, inner pores 

 slightly elongated transversely, outer pores slitlike. 



Periproct. — Inframarginal, on slight oblique truncation, tear-drop 

 shaped, with apex pointing adorally, width approximately equal to 

 length. 



Peristome. — Anterior, pentagonal, slightly higher than wide. 



Floscelle. — Bourrelets strongly developed, toothlike. Phyllodes 

 double pored, very broad and large, deeply depressed between bourre- 

 lets ; one series of pore pairs in each half -ambulacrum (chart 3, fig. k) 

 with wide space between series; pore pairs widely separated from 

 edge of peristome; no buccal pores. 



Tuherculation. — Tubercles on adoral surface larger than those on 

 adapical surface. 



Occurrence. — Cretaceous (Cenomanian) at Coulaines, Canicus a 

 Yore, Le Mans, and Fouras in France, and Lyme, England. 



Location of type specimen. — Lectotype in ficole des Mines, Paris. 



Remarks. — d'Orbigny established this genus for the species P. 

 (Pygitrits) lampas and P. (Pygitriis) rostratus and distinguished 

 Echinopygiis from Pygurus on just one character: the periproct is 

 transverse in Echinopygiis but longitudinal in Pygurus. Desor (1857, 

 p. 310) and Cotteau (1867, Pal. franc, Jur., p. 128) considered that 

 this difference was not of sufficient importance to warrant generic 

 distinction. Lambert and Thiery (1921, p. 355) did not consider 

 the periproct to be transverse and considered the two genera to be 

 synonymous, but because they thought the name Pygurus was pre- 

 occupied, they substituted Echinopygus for Pygurus. Mortensen 

 (1948, p. 133) pointed out correctly that the name Pygurus was 

 available to Agassiz because Dejean's (1833) Pygurus was a nomen 

 nudum. Mortensen disagreed with Lambert and Thiery and stated 

 that the periproct was transverse in P. lampas and cited d'Orbigny's 

 (1856, pi. 919, fig. 2) figure in which the periproct is shown as being 

 much wider than high. From my own observation of specimens of 

 P. lampas, the width of the periproct is approximately equal to the 

 length. In P. rostratus, however, the periproct is definitely wider 

 than high. However, it is so similar in all its other characters to the 

 type species of Pygurus (Pygurus) , P. montmollini, that I believe 

 it should be considered as congeneric with Pygurus. 



