NO. 3 CASSIDULOID ECHINOIDS — KIER 35 



posterior margin, in slight groove extending from apical system to 

 posterior margin. Opening longitudinal. 



Peristome. — Anterior, pentagonal. 



Floscelle. — Bourrelets well developed, inflated. Phyllodes not wid- 

 ened (text fig. ii), double pored, very long, extending almost to 

 margin, pore pairs arranged in three series in each hal f -ambulacrum ; 

 no buccal pores. 



Occurrence. — Jurassic (Bajocian) of England and France. 



Location of type specimen. — Probably in the British Museum 

 (Natural History). 



Remarks. — The two specimens I studied came from the same 

 locality and are without doubt the same species, but their apical 

 systems are not similar. In one, there are no catena! plates joining 

 the apical system to the periproct, and in the other the catenal plates 

 are numerous and the posterior oculars are prolonged (see text figs. 

 12, 13). The presence of catenal plates is a variable feature in this 

 species and is obviously not of as great taxonomic importance as 

 has been considered. 



Pomel stated that this genus differed from Clypeus in having 

 shorter posterior ocular plates, and in having the periproct more 

 distant from the apical system. He referred three species to the 

 genus, Clypeus hugi Agassiz, Niicleolites agassizi Wright, and 

 Echinites suhulatus Young and Bird. Lambert and Thiery (1921, 

 p. 344) maintained the genus as described by Pomel, but later (1925, 

 p. 586) restricted the genus to species having the apical system 

 joined to the periproct by a series of plates. They transferred 

 C. hugi and E. suhulatus to Clitopygus. The short posterior ocular 

 plates, however, and the small plates joining the apical system to the 

 periproct are not valid generic characters, because they are variable 

 within the type species. The two specimens I studied of Clypeus 

 agassisi came from the same locality and are similar in all respects 

 except that in one the posterior oculars are short and there are no 

 plates joining the apical system to the periproct (text fig. 12), but 

 in the other the posterior oculars are very long and are joined to the 

 periproct by a series of plates (text fig. 13). Furthermore, I have 

 found this same variation in specimens of Niicleolites scutatus (text 

 figs. 30-32). C. agassisi has strikingly similar petals, peristome, 

 bourrelets, and phyllodes to those of the type species of Clypeus, C. 

 plotii, and differs only in having a more inflated test, and its periproct 

 more distant from the apical system and not in a deep groove. These 

 differences do not warrant generic separation, and Crotoclypeus is 

 herein considered a junior subjective synonym of Clypeus. 



