NO. 3 CASSIDULOID ECHINOIDS — KIER 57 



Comparison ivith other genera. — Nucleolites is distinguished from 

 Clypeopygus by its lower test, and from Phyllobrissus by its wider 

 test, less developed bourrelets, and more anterior periproct. 



Remarks. — The apical system is variable in Nucleolites, not only at 

 the generic level but also at the specific. I studied a collection of 

 specimens of N. scutatus Lamarck all from the same locality, in which 

 in seven of the specimens the sutures in the apical systen» were 

 visible. In four of them genital 2 (text fig, 30) was short, not 

 extending far enough posteriorly to separate genital plates 4 and i, 

 and there were no catenal plates. In one of them (text fig. 31) 

 genital 2 is more elongate posteriorly and separates genital plates 

 4 and I, and in one of them there are numerous catenal plates (text 

 fig. 32) joining the posterior ocular plates to the periproct. Although 

 no complementary plates occurred in any of the seven specimens, both 

 Cotteau (1872, Pal. franc, Jur., pi. yy, fig. 5) and Beurlen (1933, 

 p. 58) found them in other specimens. In some species there are 

 specimens with many complementary plates as in A'', orbicularis 

 (Phillips) (text fig. 2^) and A^. major (Agassiz) (text fig. 34), 

 few as in a specimen of A'^. burgundiae (Cotteau) (text fig. 36), and 

 none as in a specimen of A^. httgi (Agassiz) (text fig. 35). Genital 2 

 is often small, not extending posteriorly between genital plates 4 

 and I, as in a specimen of A'', scutatus (text fig. 30), or very large, 

 extending not only between the posterior genital plates but also 

 between oculars V and I, as in a specimen of A^. brodici (Wright) 

 (text fig. 37). 



The phyllodes, on the other hand are remarkably consistent within 

 the genus. There are always two series of pore pairs in each half- 

 ambulacrum, usually with approximately 10 in each outer series and 

 4 to 6 in each inner, as in A^. gracilis (Agassiz) (text fig. 38), N. pla- 

 ccntula (Desor) (text fig. 39), A^. lorioli (Cotteau) (text fig. 40), 

 A^. rotundus (Peron and Gauthier) (text fig. 41), A'', ampins Agassiz 

 (text fig. 42), A^. orbicularis (Phillips) (text fig. 43), N. burgundiae 

 (Cotteau) (text fig. 44), A'', major (Agassiz) (text fig. 45), N. 

 clongatus Agassiz (text fig. 46), N. scutatus Lamarck (text fig. 49), 

 and A^. subquadratus Agassiz (text fig. 48). In A'', hugi (Agassiz) 

 (text fig. 47) the phyllodes are similar except that they are longer, 

 having approximately 18 pore pairs in each outer series and 6 to 8 

 in each inner. 



Desor's Echinobrissus placentula from the Aptian is a Nucleolites 

 and not a Nucleopygus as determined by Lambert and Thiery (1921, 

 p. 347). The phyllodes (text fig. 39) are double pored on a specimen 



