116 PROCEEDINGS OF THE NATIONAL MUSEUM vol. 81, art. 12 



strongly recurved and sharply pointed marginal claws, usually num- 

 bering two, occasionally three or more, on the external side of the 

 disk. 



Oxyhexasters represented by hemihexactinic and somewhat less 

 frequently by hexactinic forms, are abundantly present in the choano- 

 some as well as in the gastral layer. Normally developed oxyhex- 

 asters (fig. 16, /) may frequently appear in the choanosome, measur- 

 ing 130/A to 140/x in diameter. From each exceedingly short prin- 

 cipal there diverge two, occasionally three, slightly rough-surfaced 

 and nearly straight terminals. Hexactinic forms (fig. 16, e) (axial 

 length 120/x) are for the most part appreciably smaller than the 

 hemihexactinic. It seems to be the general rule that the oxy- 

 hexasters show a tendency to take the hexactinic form. The ter- 

 minals ajopear to be moderately thin and are generally nearly 

 straight. In the hemihexactinic forms (fig. 16, g) usually five, but 

 sometimes one, of the six principals are uniterminal ; the rest of the 

 principals are biterminal, in which case the entire ray is either 

 straight or else is bent at the base. A case of a. principal bearing 

 more than two terminals has not been observed. 



Microdiscohexasters of 30/x and 40/i, in diameter are sparsely dis- 

 tributed in the dermal membrane as well as in the choanosome. 

 They are quite similar to those occurring in R. ung^iculatus, except 

 in having a greater diameter. 



RHABDOCALYPTUS VICTOR Ijima 



Rhahdocalyptus victor Ijima, Annot. Zool. Japon., vol. 1, p. 52, 1897. — Ch. 

 Gkavier, Bull. Mns. d'Hist. Nat. Paris, vol. 5, no. 8, p. 421, 1899.— Ijima, 

 Journ. Coll. Sci. Imp. Univ. Tokyo, vol. 18, art. 7, pp. 238-253, pis. 18, 19, 

 figs. 1-23, 1904. 



Two small fragments in this collection, which probably belong to 

 the same colony, were obtained at the entrance of the Uraga Channel, 

 at a depth of 200 fathoms (Station 5090). In these specimens I 

 found much larger and stronger parenchymal prostalia than any 

 hitherto recorded, attaining a length of 30 mm to 40 mm and a width 

 of I70fj. at the middle. The discoctaster usually measures ISOfx in 

 diameter, and frequently larger ones, measuring 220/x in diameter, are 

 found on the gastral layer intermingled with the smaller. It may be 

 somewhat worth while to mention that the meshed siliceous reticulum, 

 which seems to be homologous to that of basidictyonal plate in its con- 

 titution and formation, is occasionally present on the surface of the 

 large parenchymal diactins to which it is attached. The foundation 

 of this network is made up of certain stauractins, hexactins, and 

 pentactins, synapticularly fused together. 



