1881.] PROF. F. J. BELL ON THE GENUS ASTERIAS. 503 



The more we get into subdivisions the more unsatisfactory will, it 

 is obvious, our characters get ; and I fully recognize the difficulty, 

 nay, impossibility, of naturalists having any thing like a unanimous 

 opinion on the value of the groups now to be proposed. I give 

 them, however, for what they are worth. They depend on the cha- 

 racters of the spines on the abactinal surface ; and, according as these 

 are simple or rare, blunted or acute, we may get divisions to which 

 we may apply the epithets of simplices, rnrispinosce, obtusispinosce, or 

 acutis2'>inosce. This unsatisfactory method of division is, at present, 

 the only one which can be suggested for the Monacanthid Pentacti- 

 nida. 



When applied in tabular form, we get the following as the result 

 of our attempt : — 



Genus Asterias. 

 Div. I. HETERACTINIDA. 



Species with, as a rule, more than five rays. 



A. POLTPLACIDA. 



Species with more than one madreporic plate. 



i. MONACANTHIDA. 



Adambulacral spines in a single longitudinal row. 



a. ECHINOPLACIDA. 



Madreporic plate with a circlet of spines. 

 0. 



ft. Anechinoplacida. 

 No circlet of spines to madreporic plate. 



(i.) Autacanthida. Dorsal spines placed on special plates. 

 A. tenuispina. 



(ii.) Typacanthida. Dorsal spines not placed on special plates. 



A. calamaria. 



ii. Diplacanthida. 



Ambulacral spines in a double row, 



a. ECHINOPLACIDA. 

 0. 



ft. Anechinoplacida. 

 (i.) Autacanthida. 

 0. 



(ii.) Typacanthida. 



A. acutispwa. A. pohjplax. 



A. capensis. 



