NO. 3 CASSIDULOID ECHINOIDS — KIER I45 



are more developed, and the peristome is more central. The later 

 species of Hardouinia have much wider, shorter phyllodes with even 

 more developed bourrelets and are easily distinguished from Petalo- 

 brissus. 



Hardouinia is similar to Siiguiafopygiis in the shape of its test, 

 position of periproct, prominent bourrelets, and phyllodes, but differs 

 from it by the absence of a deep transverse groove ventral to the 

 periproct, a central peristome, and generally broader petals. 



Lambert and Thiery (1921, p. 361) consider Hardouinia a subgenus 

 of Procassidulus (herein considered a synonym of Rhynchopygus) . 

 This genus, however, is quite distinct from Rhynchopygus, having a 

 much larger, more inflated test, and much broader petals. Lambert 

 and Thiery give the age of all the American species they refer to this 

 genus as Eocene or Oligocene, but they are all Upper Cretaceous. 



Cooke (1953, p. 19) considered AustralantJius a synonym of Har- 

 douinia, but in Australanthus the petals are more open and generally 

 narrower, the apical system is monobasal, and the phyllodes are nar- 

 rower with far fewer pores. 



Evolution. — The species of this genus range from the Turonian to 

 the Maestrichtian, with a conspicuous evolutionary trend in the struc- 

 ture of the phyllodes and the bourrelets. The phyllodes become 

 broader, shorter, with fewer pores in the inner series. This reduction 

 of pores in the inner series is away from the peristome with the first 

 pore in the inner series progressively becoming more widely separated 

 from the peristome. In order to avoid subjective selection of species 

 which would favor confirmation of this trend, I have studied the 

 phyllodes of all the known species of Hardouinia, in which this area 

 is preserved. They are all figured on chart 7. The age determinations 

 on the species were made by Dr. Norman F. Sohl of the U. S. Geo- 

 logical Survey, who has made detailed studies in the stratigraphy of 

 the Upper Cretaceous in the region where these species occur. 



In the earliest known species, H. stantoni (Clark) from the Turo- 

 nian, the phyllodes (chart 7, fig. a) are slightly widened, long, with 

 two series of pores in each half -ambulacrum, with numerous pores 

 in the inner series. In the Santonian species, H. hasslcri (Twitchell) 

 (chart 7, fig. b), the phyllodes are considerably wider and shorter 

 with approximately the same number of pores in the inner series as 

 in H. stantoni. In H. clypeus Cooke, also of Santonian age, the phyl- 

 lodes (chart 7, fig. c) are of similar width and length as H. hassleri, 

 but there are more pores in the outer series and they are irregularly 

 arranged. In H. potosiensis Lambert, from the Campanian, the phyl- 



