NO. 3 CASSIDULOID ECHINOIDS — KIER 25 



Material. — Two specimens studied in the U. S. National Museum 

 collections, one in the Ecole National Superieure dcs Mines, Paris, 

 and nine in the British Museum (Natural History). 



Shape. — Medium to large size; outline varying from circular, to 

 wider than high, flattened, with low, smoothly domed adapical sur- 

 face, slightly depressed adoral surface; ambulacra on adoral side 

 slightly depressed. 



Apical system. — Central, tetrabasal, genital plates arranged in 

 semicircle anterior to opening of periproct. 



Ambulacra. — Petals very slightly developed (pi. i, fig. 4), posterior 

 petals flexuous; all petals extending almost to margin; pores not 

 conjugate ; outer pore slightly elongated transversely, inner round. 



Periproct. — Supramarginal, in contact with apical system, longi- 

 tudinal, with groove extending from opening to posterior margin. 



Peristome. — Anterior, slightly pentagonal. 



Floscelle. — Bourrelets slightly developed ; phyllodes (text fig. 2) 

 double pored with many pore pairs, arranged in three series in each 

 half -ambulacrum, with six or seven pore pairs in each series ; no 

 buccal pores. 



Tuberculation. — Tubercles perforate, crenulate, not arranged in 

 vertical series ; slightly larger adorally than adapically. 



Occurrence. — Middle Jurassic (Bajocian to Bathonian) of Eng- 

 land and France. 



Location of type specimen. — Unknown. 



Synonym of GALEROPYGUS 



Rcssopygiis Pomel, 1883. Class, meth., p. 56. Type species by subsequent desig- 

 nation, Mortensen (1948, p. 109), Clypcus constantini Cotteau. 



Remarks. — I found a topotypic specimen of this species in the 

 Lambert Collection at the Sorbonne, Paris. The specimen is not well 

 preserved but the phyllodes are visible, and a drawing of one of them 

 is included in text figure 3. Since this specimen shows no features 

 not visible on Cotteau's (1873, Pal. franc, Jur., pi, 6t,) original 

 figures, I do not include a description of it. 



Both Lambert and Thiery (1921, p. 336) and Mortensen (1948, 

 p. 109) considered Ressopygus a synonym of Galeropygus. The type 

 species of both genera are very similar, each having a large broad 

 test, with narrow ambulacra, slightly developed petals, phyllodes with 

 many pore pairs arranged in three series, and a supramarginal peri- 

 proct in contact with the apical system. They dififer in that in G. 

 constantini petals V and I distally curve posteriorly, whereas in 



