ACTINOSTOME. fig 7 



as Faorina (PL XIX n .f. 5, 6), Linthia (PL XIX a .f. 8, 9), and Brissus (PL 

 XXI". f. 2, s) ; less marked, and at the same time the opening is more 

 circular, in Breynia (PL XV." f. s, 9), Eupatagus (PL XV". f. 3, 4), and Platy- 

 brissus (PL XXP f. .3, 4) ; while in the Cassiduloids, in which the actino- 

 stome has become pentagonal, the sides are all on one level (PL XV. f. 3), 

 and the actinal membrane is covered by a coating of numerous small plates, 

 leaving a central opening (PL XVI. f. 9). In some genera, the interambula- 

 cral spaces between the phyllodes are crowded with minute tubercles, forming 

 what are called bourrelets (PL IF*. /. 2; PL XV. f. a), or the ambulacra 

 remain simple pairs of pores, as in Echinoneus (PL XV. f. e), round the 

 actinostome, forming an approach to the structure of the true Clypeastroid 

 actinostome. A very anomalous structure of the actinostome occurs in 

 Paleostoma, where the actinostome is pentagonal, and covered by a small 

 number of plates radiating from the actinostome (PI. XXXII. f. 14). See 

 Part III. p. 582. 



