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BULLETIN 93, UNITED STATES NATIONAL MUSEUM. 



and indeed in the specimens of B. amaryttis which I have dis- 

 sected. B. albus and B, tennis seem to be sufficiently distinct for 

 specific separation. Unfortunately, the sutural edges and the basis 

 have not been sufficiently investigated in the small species closely 

 related to B. crniaryllls, obtained by the K'iboga- Expedition. We 

 know that in B. amaryllis the basis is porous, and the edges of the 

 radii are crenulated; but these characters are unknown in B. Tjimce, 

 B. maculatus, and B. albus. B. tennis has a poreless basis and 

 smooth, thin edges of the radii, and is therefore quite distinct from 

 B. aanaryllis. 



ATJSTROBALANITS, new subgenus. 



Walls solid, poreless, their basal edges roughened with irregular 

 points and ridges (except in B. vestitus] ; basis calcareous, some- 

 times extremely thin; radii narrow or wanting; the sutural septa 

 irregular. Scutum with the adductor ridge long and strong, and 

 usually with crests for the lateral depressor muscle. 



Type. Balamis imperator Darwin. 



The species composing this subgenus are very distinct from one 

 another. Further investigation of the cirri is needed. 



KEY TO SPECIES. 



a 1 . Interior of walls and valves of a fine violet color, the basal edge of wall 

 thick, with dense sculpture of fine ridges and points. Scutum with irreg- 

 ular crests for both rostral and lateral depressor muscles ; spur of tergum 

 rounded distally ; rather large B. imperator Darwin. 



