GENERA AND GROUPS OY THE ECHTNOfDEA. 217 



It has often been attempted to arrange tlie very numerous 

 genera, both, fossil and recent, of tbis Family into subfamilies, 

 but with very doubtfal success, on accouut of the presence of 

 intermediate forms. 



The researches of Loven have indicated that the least artificial 

 method of classificatiou, and one which is comparatively natural, 

 is to rely upon the subaual fascicle and its complementary modi- 

 fications of the posterior ambulacra and their tentacles as a 

 taxonomic character of importance, and to consider the other 

 fascioles in a secondary sense. 



Division I. The Adetes. All fascioles absent. 



II. The Prymnadetes. Subanal fasciole absent, other 

 fascioles present. 



III. The Prymnodesmia. Subanal fasciole present. 



IV. The Apetala. Tests with flush, apetalous, usually 



uniporous ambulacra. 



I. Division Adetes. 



Genus Isaster. 



Epiaster. 

 Subgenus Macraster. 

 Genus Echinospatagus. 



Ennalaster. 



Heterolampas. 



Megalaster. 



Hemipatagus. 



Platybrissus. 



Palceopneustes. 



Grenus Isaster, Desor, 1858, Synopsis, p. 359. De Loriol, 1888, 

 Pal. de la Province d' Angola, W. Africa, Ech. p. 118, 

 pi. viii. 



Test moderate in size, elongate, eordiform, largest in front, 

 contracted posteriorly. 



Apical system compact, slightly excentric in front. 



Ambulacra slightly diverse, in shallow depressions, long, sub- 

 equal ; the anterior with smaller pores than the others, its pores 

 elongate, forming a subpetaloid open area ; the posterior ambu- 

 lacra resembling the anterior pair, but less divergent, the pores 



