SÏAUROCALYPTUS AFFINIS. 189 



The discodaêters occur in tlie sabdermal space as well as 

 near the gastral surface. They are not very abundant, though in 

 places several are found together. Right in the choauosome they 

 must be very rare, if indeed they are ever present. Two sizes 

 are distinguishable according to their position. The smaller disc- 

 octaster form (PL XIII., lig. ö), measuring 120-200/^ (in the 

 second specimen, 160-183 ij) in diameter, occurs only in the 

 subdermal space ; while the larger (PL XIII., fig. 6) of 280- 

 400/^ (in the second specimen, 350-380 /j) is confined to the 

 proximity of the gastral surface. The range of variability in the 

 size of discoctasters is here decidedly wider than in either -'S'. 

 dowlingi or S. tubulosus. 



As to general shape the discoctasters in general closely agree 

 with those of several other nearly allied Staurocalyptus species 

 and also with those of Acanihascus cactus. The principals take 

 up i-'s of the entire ray-length, are unevenly contoured, thicken 

 somewhat in the outward direction and carry a slightly expanding 

 tuft of 3-7, straight or nearly straight terminals. The central 

 node, especially that of the smaller discoctasters, frequently shows 

 the six well-known tubercles. In the larger form, the distal 

 portion of the terminals is beset with minute but distinct barbs 

 (fig. G) and the terminal disc exhibits a number of marginal teeth 

 exactly as I have figured them from Acanihascus cactus (PL 

 XI r., fig. 28). In the smaller form, the terminals are simply 

 rough and the terminal discs pinhead-like. 



The discoctaster as well as the oxyhexaster, — of the latter, 

 both the normal and the hexactinose forms, — I have subjected to 

 special examinations in order to determine the position and extent 

 of the central cross of axial filaments in the central node. The 

 results are embodied in PL XIV., figs. 23-20, which will speak 



