Marine Sponges from Japan. 401 



four arms smooth, but of course very variable. Nos. t and 2 

 are chiefly confined to the dermal sarcode, where, in great 

 abundance, they cover the nail-like disks, inside which, 

 among the branched forms of the staple spicule, the acerates 

 no. 3 appear in bundles, finally becoming lost inwards or 

 only sparsely present as the staple spicule becomes developed 

 into its ultimate or interlocking form. For analogous tran- 

 sitionary forms of development into which the simple disk 

 (fig. 11, a, b) passes on its way to produce the entire spicule 

 I must refer the reader to my delineations of Discodermia 

 papillata &c. (' Annals,' 1880, vol. vi. pi. viii. fig. 48, &c), 

 as there is no room in my plate for a repetition of this here. 



Hab. Marine. 



Loc. Japan, Misaki, at the entrance of the Bay of Tokio 

 (Yedo). 



Obs. This is the species to which Zittel has given the name 

 of "Racodiscula" illustrated by the " trilobate " form of the 

 staple spicule, together with some of the long acerates, broken 

 off at the ends, as they generally present themselves in a 

 fragment mounted in balsam in its natural state, together with 

 some of the minute ellipsoids (Abh. d. k. bayr. Akad. ii. 

 CI. Bd. xiii. 2, 1878, p. 151, Taf. i. fig. 8, and ' Annals,' 

 1878, vol. ii. p. 480), which came from a vasiform thick- 

 stemmed specimen about 4^ in. high, 4^ in. across the brim, 

 and 3 in. deep in the excavation, also obtained from Japan. 

 The presence of the minute ellipsoid makes it differ from all the 

 species from the Gulf of Manaar whose respective spiculations 

 1 have illustrated (' Annals,' 1880, vol. vi. pi. viii.) ; but the 

 transformation of the surface-disk into the branched and fili- 

 greed, staple, tetractinellid spicule is the same, whereby it can 

 be seen that the trilobate form given by Zittel as illustrative of 

 his genus u Racodiscula " is of no specific value, nor is the long 

 acerate spicule no. 3 (fig. 11, e), which is found in many species 

 and which Prof. Sollas discovered and first pointed out in the 

 fossil genus Siphonia (Quart. Journ. Geol. Soc. Nov. 1877, 

 p. 808, pi. xxvi. figs. 5 and 5 a) ; but in no instance, I 

 believe, have the minute spicules nos. 1 and 2, together with 

 the earliest discoid forms of the tetractinellid (which led to 

 Bocage's designation "Discodermia" in the recent species), 

 been discovered in situ in the fossilized specimens, being too 

 delicate probably to survive this transitionary ordeal. The 

 general form and structure of Dr. Hinde's Trachysycon 

 nodosum ( l Catalogue of Fossil Sponges in the British Mu- 

 seum,' 1883, pi. xii. figs. 3 and 3 b) very much resembles the 

 species above described. 



