EHABDOCALYPTUS UNGÜICÜLATUS. 273 



No cliactins seem to occur as hypodernialia, unless those tliat 

 occasionally extend from the choanosome into the ectosome or 

 unless those which will presently be mentioned as unusually 

 elongate dermalia be regarded as such. 



The dermalia (PI. XXI., fig. 2) are nearly exclusively diactins 

 and only occasionally stauractins or tauactins. The rays are rough 

 all over and slightly tapering towards the rounded or obtusely 

 conical end. The diactins are nearly straight or only perceptibly 

 arched. In them the center is usually not marked by any 

 swelling ; only occasionally it is indicated by tw^o opposite lateral 

 tubercles, never by four such in ci'uciate disposition, — a fact which 

 suggests the direct derivation of the diactins from stauractins and 

 not immediately from either pentactins or hexactins. The diactinic 

 dermalia generally measure 330-420 ,« (about 400 /^ on an average) 

 in total length and 8-15 !'■ (about 10 <" on an average) in thickness 

 near the middle. Rarely there occur, among the dermalia, di- 

 actins, 800 /^ or nearly 1 mm. long. With such an increase in 

 length of the dermalia, the roughness of the surface shows a 

 tendency to become confined to the terminal parts, leaving the 

 middle parts smooth. 



The gastralia (PI. XXL, fig. 3) are rough oxyhexactins of 

 much greater axial length than the dermalia. They are con- 

 siderably larger than the same spicules of R. mollis. The radial 

 axis is 640-850/^ (on an average about 780/^) long. Length of 

 the free proximal ray, 440-550 (j- ; that of the distal ray, 230- 

 300 /^ ; that of paratangentials, 275-330 /a Thickness of rays 

 near base, about 15/^ on the average. The proximal ray, which 

 is not only the longest but generally also the thickest of all in 



