ASTHENOSOMA. 171 



ASTHENOSOMA. 

 Grube, 18G8. 45 er Jahres-Bericlit d. Schles. Gesell, p. 42. 

 Type-species, Asthencsoma varium Grube, 1. c. 



After careful consideration it has seemed desirable to limit Astheno- 

 soma, as Mortensen proposed, to the species on which Grube based the 

 genus and its nearest allies. They are characterized by a rather firm test 

 having the actinal side markedly different from the abactinal. The coronal 

 plates of the upper side are very low and wide, each witli a horizontal series 

 of 5-20 small primary tubercles, none of which are noticeably larger than 

 the others. The abactinal primary spines are small and numerous, and are 

 encased in loose skin-sheaths. The actinal tube-feet have well-developed 

 sucking-discs. The sphteridia are more or less elongated and occur only on 

 the inner (lower) secondary plate-element. In this limited sense Astheno- 

 soma includes at most only four species, and probably only two. The evi- 

 dence accumulated by de Loriol, Dbderlein, and de Meijere seems to prove 

 that A. Grubei A. Ag. is really a synonym of varium Grube, as Agassiz 

 himself suggested in 1881 ("Challenger" Echini, p. 84). From the descrip- 

 tions and figures which have been published we are strongly inclined to 

 consider A. urens Sarasins and A. heteractis Bedford as also synonyms of 

 varium, but as we have no material at hand for comparison, we let them 

 stand for the present as distinct. The following table shows how closely 

 related the four accepted species are : 



Actinal primaries more or less distinctly banded (usually greenish banded 

 with purple). 

 Auibulacral primary spines, abactinally, much longer than those of inter- 

 ambulacra but not markedly unlike them in color. 

 Naked radial areas of abactinal surface, relatively narrow, or want- 

 ing ; that of median interambulacral field not exceeding .10 of 



interambulacrum rarium. 



Naked radial areas of abactinal surface, conspicuous ; that of median 



interambulacral field exceeding .20 of interambulacrum .... urens. 

 Ambulacral primary spines, abactinally, about equal to those of interam- 

 bulacra, markedly different from them in appearance, the sheaths being 



very distinctly and regularly banded with purple heteractis. 



Actinal primaries white and unhanded Ijimai. 



