ARISTOTLE'S LANTERN AND PERIGNATHIC GIRDLE. 

 HL 



197 



234 



Text-figs. 231-236. — Base of corona with att,aclmicnt of lantern muscles in the Clypeastrina. 



231. Clypeaster subdepressus {GTa,y). West Indies. R.T.J. Coll., 887. X 2.8. Ainbulacral plates nearly roof over 

 the primordial interambulacral plates. Auricles are high, bearing the insertion of the protractor and two pairs of retractor 

 muscles. 



232. The same. X 4.7. Showing the relat ion of jninionlial ambulacral and inteiambulacral plates, the latter shaded. 



233. Clypeaster rosaceus {hmn6). Bahamas. H. T. J. Coll., 888. X 5.7. The primordial interambulacral plate is 

 less completely covered by the ambulacrals than in text-fig. 232. 



234. The same. Plates separated, inner view (p. 74). 



235. The same. Plates separated, viewed from peristome. 



236. Echinarachnius parma (Lamarck). Eastport, Maine. X about 5.7. Auricles are transferred to the primordial 

 interambulacral plate and bear the insertion of protractor and one pair of retractor muscles. 



Lettering as in text-figs. 221-230, p. 193. 



