Asterias. RADIATA. ASTERIAD.E. 485 



ASTERIAD^. 



a. Arms simple. 

 Asterias. 

 Ophiura. 



aa. Arms divided. 

 Astrophyton. 

 Comatula. 

 Marsupites. 



Gen. IX. ASTERIAS. — Suckers in rays on the oral disc. On 

 the dorsal aspect the covering is warty or spinous, and 

 more or less porous. Towards the middle there is a pro- 

 cess variously marked, analogous to the wart of the pel- 

 vis in the Echinidce. The oral surface is distinguished 

 bv the mouth in the centre, from which the avenues of 

 pores diverge, in number similar to the divisions of the 

 body, and protected by spines or warts. The rows of 

 pores in these avenues vary according to the species. In 

 the interior, and corresponding with these avenues, there 

 is a subosseous complicated skeleton. The mouth leads 

 into a stomach, from which diverge two caeca, correspond- 

 ing with each avenue. These ramify as they proceed, and 

 each is accompanied by a mesentery. There are likewise 

 two ovaria accompanying the caeca. They reproduce 

 their lost parts easily. Even a single ray we have wit- 

 nessed in the act of generating a mouth and new rays. 

 The specific characters are defective, and, wher^ obtained 

 from dried specimens, are apt to vary so much, as to lead 

 to the erection of spurious species. Even in live ex- 

 amples, the state of repletion influences the general appear- 

 ance. When dried, the length of time in which they have 

 been macerated in water, or the manner in which the ani- 

 mal has expired, in reference to its suckers or spines, all 

 tend to produce varieties of expression. 



* Margin of the body pentagonal • 



. 17. A. eart'daginea. — Body flat, thin, and reticularly verru- 



cose, with diverging obsolete rays. 



Palmipes stella cartilaginea Aldrovandi, Linck, Stell. 29. t. 1 — Ast. pla- 

 centa, Penn. Br. Zool. iv. 62, No. 59, t. xxxi — A. membranacea, Turt. 

 Brit. F. p. 140, No. 125 — Coast of England. 



