NO. 3 CASSIDULOID ECHINOIDS — KIER 1 3 



genera as Hardouinia, Rhynchopygiis, Lefortia, Clypeolampas, Faii- 

 rastcr, Domechinus, and Hypsopygastcr. In some species such as 

 Hardouinia porrectiis (Clark) (pi. 21, fig. 5) the bourrelets are 

 huge, and toothlike. After the Maestrichtian, bourrelets are never 

 as well developed, and except for the Eocene Australanthus longianus 

 (Gregory) the bourrelets never even approach in size the ones found 

 in the Maestrichtian species. 



The function of the bourrelets is to aid the echinoid in food 

 gathering. Bourrelets are covered with many small spines which 

 are used to push food particles up into the mouth. 



PERIPROCT 



In the earliest cassiduloids such as Clypeus and Nucleolites the 

 periproct is usually supramarginal, often in contact with the apical 

 system. By early Cretaceous time, however, there are many genera 

 with the periproct already marginal or inframarginal such as Pygau- 

 lus, PygorhyncJms, Astrolainpas, and Catopygus. In the Turonian 

 and Cenomanian, most of the genera have marginal or inframarginal 

 periprocts, but in the Senonian with the advent of the CassiduHdae, 

 and in the Tertiary, there are many species again Avith supramarginal 

 periprocts, but in none of them is the periproct as anterior and near 

 the apical system as in the earliest cassiduloids. 



It is obvious why the periproct and anal opening shifted away from 

 the apex of the echinoid. With the development of petals and the 

 subsequent shifting of the respiration function from the gills to them, 

 it was necessary that the anal debris not be discharged over the petals. 



PERISTOME 



In the Jurassic cassiduloids, the peristome is usually slightly 

 anterior, pentagonal, and with the length equal to the width as in 

 Clypeus, NticlcoUtes, and Galeropygiis. In the Early Cretaceous the 

 peristome is either wider than long or very often oblique as in 

 Pygaidus, Pygorhynchus, and Py go pistes. The long axis of this 

 oblique peristome is from left anterior to right posterior. The reason 

 for this obliquity is not known. From the Senonian to the Recent, 

 there are no more species with an oblique peristome, and most of 

 the Late Cretaceous and Tertiary genera have a pentagonal peristome 

 usually wider than high. 



