472 BULLETIN 100, UNITED STATES NATIONAL MUSEUM. 



At station D 5593, a vasiform sponge GO mm. high, cloaca 30 mm. 

 deep. Desma tetracrepid. 



******* 



Hentschel (1912, p. 306) has described a new form, Lophacanthus 

 rhabdophorus, which he points out does not fit in any of the families 

 as these at present are defined. Pending some better arrangement, 

 an appendix to the Theonellidae might be created for it to include 

 forms without microscleres. The triaene concept of the family, 

 already extensive, would have to be further enlarged to include 

 mesolophotriaenes with degenerate rhabdome. 



Order KERATOSA. 



Ceraosi)o»giae O. Schmidt, 1862, p. 19. 



Keratom Hyatt, 1875, p. 399.— Polejaeff, 1884, p. 38. 



Ccratosa Ridley, 18S4, p. 37S. 



Ceratvna Vosmaer, 1887, p. 362. 



Mofioceratina part plus Hexaceratina part, Lendenfeld, 1S89. 



En ccratosa Bendy, 1905, p. 200. 



Skeleton made up of horny fibers. Without proper spicules. Ab- 

 sence of spicules primitive 'and not due to evolution by loss. Sand 

 grains and other foreign mineral particles often aid in forming the 

 skeleton, and in exceptional cases constitute its chief part. 



The families included are the Darwinellidae (Aplysillidae of some 

 authors, Darwinellidae plus Aplysillidae of Lendenfeld. 1889), 

 Pleraplysillidae Topsent (see George and Wilson, 1919, p. 166), 

 Spongelidae, and Spongidae. 



The group of true horny sponges, without proper spicules, was 

 early recognized and embodied in the systems of Grant (1826, 1861) 

 and Xardo (1833). Bowerbank's Keratosa (1864, p. 155), on the 

 other hand, was made to include some sponges with proper spicules. 

 The same is true of the Keratospongia of Gray (1867). Carter 

 (1875) recognized the true horny sponges, but split them in two 

 groups, Ceratina and Psammonemata, distinguished chiefly by quan- 

 titative differences in the foreign contents of the fibers. 



Lendenfeld's monograph (1889) remains as the all-important 

 handbook for practical work on the horny sponges. But his Hexa- 

 ceratina, it would seem, should be deleted, and D a.rwinella, Aply- 

 silla, Iaitthclhi. Dendrilla, HaddoneUa (Igerna Sollas, 1903) com- 

 bined with Megalopastas Dendy in the Darwinellidae (in the mat- 

 ter of the terminology of this family see George and Wilson, 1919, 

 p. 164), as advocated by Dendy. Lendenfeld's Monoceratina is dis- 

 tinctly stated to be a polyphyletic group*, and is therefore made to 

 include forms with spicules and forms in which the spicules have 

 obviously been lost, all conceived as transitional types from different 



