CAULOPHACUS LOTTFOLIUM. 95 



type is especially common in the choanosorae ; in feet, it may be 

 said that almost all the discohexasters here present are of this 

 form. The terminals are exactly comparable to those of normally 

 developed discohexasters. When hexactinose, the axial length 

 may reach 115 /', showing an increase in diameter over normal 

 forms, — a flict which according to my experience, is generally 

 observable in all Ivssacine Hexactinellids having a hexaster in 

 the two varietal forms mentioned. Fig. 7 shows a case of the 

 hexactinose discohexaster, in which one of the six rays is bent 

 at base, i. e., at the junction of the terminal with the principal, 

 indicating its derivation from a dilophoiis ray by loss of one of 

 the two terminals. Fig. 17 shows the extent of the axial cross 

 in a hexactinose discohexaster, it being limited in extent to the 

 spicular center and the basal parts of the rays corresponding to 

 the original principals. 



Further variations — or possibly early developmental stages — 

 of the discohexaster are seen in unusually thin-rayed and obsoletely 

 rough or nearly smooth surfaced forms, such as are represented 

 in figs. 12-16. Transitional forms connect them with the thick- 

 rayed discohexasters, and they occur, together with these, not 

 uncommonly in both the subdermal and subgastral regions, but 

 especially in the latter. Sometimes they have all the principals 

 supplied with 2, occasionally 3, terminals (fig. 14); at other times 

 they are either hemihexactinose (figs. 12, 13, 16) or quite hex- 

 actinose (fig. 15). The terminal discs in a rosette of the kind may 

 be in appearance similar to those in the thick-rayed discohexaster, 

 except in being smaller and more weakly developed (figs. 12 and 

 13) ; or they may occasionally consist of 2-4, nearly transverse 

 or outwardly diverging, slender claws at the ends of tapering 

 terminals, in which case the rosette dçserveç tQ be çallçd au 



