PETALOSTICHA. 549 



PETALOSTICHA. 



Suborder Petalosticha IIaf.ckel, 186G, Gencrelle Morphol. (emend.) 



This third suborder contains Echini in which the ambulacra are more or 

 less petaloid, without teeth, and in which the anal system is, as in the Cly- 

 peastroids, disconnected from the apical system. The anterior and posterior 

 extremity are plainly characterized, not only by the shape of the test, but 

 also sometimes by the structure of the odd ambulacrum. The subfamilies 

 here recognized in this suborder are more easily characterized than the 

 common features of the ftunilies, which, with the exception of the few ordinal 

 features mentioned above, seem to be more negative than positive. 



In this suborder we find specializations of certain parts of the test and 

 spines carried out to a greater degree than in the other suborders ; the 

 presence of plastrons and of fascioles, which are accumulations of miliary 

 tubercles in certain lines, are characteristic of most of the genera of Spatan- 

 goicls. 



OASSIDULIDAE. 



Family Cassidulidae Agass., 1847, C. R. Ann. Sc. Nat. VII. 147. 



They differ from the Clypeastroids by the absence of teeth, and less dis- 

 tinct structure of the apical system ; ambulacra more or less petaloid. 

 Mouth pentagonal, oblique, or elliptical, central or subcentral ; in some 

 genera the pores round the actinostome are connected by furrows and form 

 elegant designs, to which the name of phj-llodes has been given. These 

 phyllodes are separated by clusters or knobs of tubercles, rising in the 

 interambulacral spaces between them, known as bourrelets ; the phyllodes 

 with the bourrelets form the floscelle. We have included in the Cassidulidae, 

 as here limited, only genera which have no plastrons or fascioles. The 

 tubercles are neither perforate nor crenulate, as they are in Clypeastroids. 

 Position of anal system variable. 



