NO. 3 CASSIDULOID ECHINOIDS — KIER 2$ 



a lantern in any adults. They differ from the spatangoids in lacking 

 fascicles, in not having a specialized plastron, and in having a floscelle. 

 Remarks. — Durham and Melville (1957, p. 260) divided the Cas- 

 siduloida into two orders : the Nucleolitida and the Cassiduloida. All 

 the genera with tetrabasal apical system and unequal pores in the 

 petals were placed in the Nucleolitoida, and all with monobasal apical 

 system and nearly equal pores in the petals were placed in the 

 Cassiduloida. This division, however, is not feasible, for there are 

 many genera such as Clypeolampas, Kephrenia, Pliolampas, Gito- 

 lampas, Rhyncholampas, and Australanthns which have a monobasal 

 apical system but have the pores of their petals very unequal. As a 

 matter of fact, there are more genera with a monobasal apical system 

 and unequal pores than with equal pores. If this biordinal classifica- 

 tion were used, many genera which are very similar in other charac- 

 ters would be separated into different orders. Cassidulus would not 

 be in the same order as its very close relative Rhynchopygus, even 

 though both genera differ only in that one has a tetrabasal apical 

 system, whereas the other is monobasal. At one time I thought that 

 the Cassiduloida could be separated into two orders on the presence 

 of one or two pores in the ambulacral plates beyond the petals and 

 in the phyllodes. However, this division would be artificial, being 

 purely morphological and not phylogenetic. Many genera closely 

 related in the sum total of their characters would be placed in sep- 

 arate orders. Parapygus and Pygorhynchus would be placed in dif- 

 ferent orders even though they are indistinguishable except for the 

 presence of single pores in Parapygus. Likewise Gentilia would be 

 separated from Archiacia, Rhynchopygus from Ochetes, and Oolo- 

 pygus from Catopygus. 



Family GALEROPYGIDAE Lambert, 191 1 



Large, circular to elongate ; apical system central, tetrabasal ; peri- 

 proct supramarginal, in contact with apical system, longitudinal, in 

 deep groove extending to posterior margin ; peristome anterior, oval ; 

 ambulacra subpetaloid, flush with test, open, long, extending almost 

 to margin ; all ambulacral plates double pored ; bourrelets absent or 

 slightly developed ; phyllodes narrow, double pored with two or three 

 series of pore pairs in each half-ambulacrum ; no buccal pores ; 

 tubercles adorally slightly larger than adapically ; no naked, granular 

 zone in interambulacrum 5. 



Genera. — Galeropygus, Hyhoclypus. 



Range. — Jurassic (Toarcian to Rauracian). 



