434 BULLETIN 100, UNITED STATES NATIONAL MUSEUM. 



shape; ends occasionally unequal, spicule becoming actually mon- 

 actinal. In one set of species however the megascleres are cylindri- 

 cal oxeas varying to strongyles of similar shape. With microscleres 

 in the form of isochelas, accompanied often by sigmas, less often by 

 trichodragmas or toxas. 



Dendy, 1921& (p. 102), points out that the genus was established 

 in 1873 by Wyville Thomson and that Carter's name Histoderma 

 is a synonym and must be retired in spite of its universal currency. 

 Dendy is evidently right and Coelosphaera must be used instead of 

 Histoderma, since Thomson's sponge, C. tubifex, is recognizably de- 

 scribed (1873, pp. 484-486, fig. 83). The habitus of this sponge 

 is phloeodictyine ; there is a smooth rind j the megascleres are " pin- 

 headed," the microscleres sigmas and isochelas. Dendy concludes, 

 moreover, that Carter's type, Histoderma appendiculatum, is specifi- 

 cally identical with this species. 



In separating Coelosphaera (Histoderma) from the haplosclerid 

 phloeodictyine sponges Lundbeck (1910, p. 28) is influenced in part 

 by the fact that the megascleres of such species as C. (Histoderma) 

 appendiculata Carter are fundamentally different from those of 

 Phloeodictyon, etc. The spicules of the latter genera are oxeas 

 varying to strongyles, cylindrical and fundamentally diactinal. The 

 magascleres of C. (Histoderma) appendiculata Carter on the con- 

 trary are fusiform or subfusiform tylotes, which only secondarily 

 become strongylate; moreover, they show their desmacidine origin 

 in an early ontogenetic stage which is monactinal (Lundbeck, 1910, 

 p. 10). This is convincing. A complication is however effected 

 by the occurrence of species like C. (Histoderma) singaporensis 

 (Carter), C. (Histoderma) vesiculata Dendy, and C. toxifera of this 

 report. In these species the megascleres are cylindrical oxeas or 

 strongyles or intermediates, which do not differ from the haplosclerid 

 type of diactinal spicule (Ridley, 1884, p. 421, Lindgren, 1898 p. 

 297, Dendy, 1905 p. 166). A curious feature, too, is that in them all 

 the megascleres show such a remarkable variation in size, more 

 especially in length. In these species, nothing in the adult spicule 

 suggests a monactinal phylogenetic origin, and while the ontogeny 

 has not been studied in detail, Ridley, 1884, interprets very slender 

 oxeas as young stages in C. (Histoderma) singaporensis and Dendy, 

 1905, mentions for C. (Histoderma) vesiculata slender hair-like 

 spicules, apparently diactinal, which are probably young stages of 

 the adult sclerites. Thus these species are set off in respect to an 

 important feature from the typical Coelosphaeras, and something 

 might be said in favor of their union with the haplosclerid Phloeo- 

 dictyinae, regarding the latter as forms in which the chelas have 



