56 



PORIFERA. r. 



Phlaeodictyon Carter. 



Tlie fonii more or less roundish, sonietmies lengtlieiicd or becoming quite irregular. The sponge 

 provided with shorter or longer tubular processes., so-called fisfuUr. The external layer marked off as a 

 harder bark., highly provided zvith spic7iles. The other siceleton may be different, formed of Jib res. or of a 

 net of single spicules or of irregularly situated spicules. Spicula are oxea, most frequently shortly pointed, 

 sometimes strongvla ; most frequently they are somnvliat curved. Spongin (often) present, but not to 

 any considerable degree. 



Carter, in 1882 (Ami. and Mag. of Nat. Hist. Ser. V, Vol. 10) established a new group Phhvo- 

 dictyina, which he chiefly characterized b>- the outer form and the presence of processes (which might, 

 however, also be wanting) as well as by a particular lamellar structure ( structure essentially laminated 

 and concentric >); he describes more particularly, how there are two different layers that ma}- alternate 

 with each other several times, but his description of this structure is not quite clear. To this group 

 he refers Oceanapia robusta Bow., Rhizochalina oleracea and carotta Schmidt (1870, Spong. atlant. Gebiet., 

 35), Rhizochalina fistulosa Bow., and some new established species. The group thus established by 

 Carter, has since been kept up as a subfamily to about the same extent given it by Carter, and 

 with slight modifications in the definition. In the meantime a number of new species have been 

 described under the genus Rhizochalina — Dendy comprises this genus and Oceanapia under the 

 name Rhizochalina — but nian\- of these species agree onl)- badly with the definition of the group 

 given by Carter, having of the characters stated by him only the external hard Ia3-er, and being 

 more or less provided with fistulas; among others this restriction holds good with regard to Rh.elongata 

 Topsent, Rh. media Thiele, and several others. At the same time several authors have called attention 

 to the relationship with Petrosia, for instance Ridley (Report on Zool. Coll. Alert 420), and Thiele 

 plainly regards his Rh. media as an intermediate form between Rhizochalina and Petrosia (Stud, iiber 

 pazif. Spong., Zoologica. X, 1897—99, ^^^^ 24, II, 19, Tab. IV, Fig. 2, Tab. V, Fig. 11). It is also scarcely 

 to be doubted that the genus Rhizochalina must be referred to the Renierince nearest to Petrosia, 

 where it has also to be referred according to its spiculation. Also in Petrosia a somewhat lamellar 

 structure may be found, as mentioned before under P. crassa; but this structure is far fi'oni being 

 found in all Rhizochalina-species, and moreover it is probably a phenomenon connected with the 

 growth of the sponge. 



As mentioned above, Rhizochali//a oleracea and carotta Schmidt are found among the species, 

 referred by Carter to PlilcBodictyina. The original specimens of both these species are in the museum 

 of Copenhagen, and by the examination of these specimens it has been seen that these two species 

 have to be referred to the Chalinincr, as has also been done by Schmidt; the fact is that they have 

 solid spongin-fibres filled with a large number of very small oxea. The concentric structure mentioned 

 by Schmidt, and which has presumably been a chief reason why Carter has referred the species 

 to Phlcrodictyina, is the same phenomenon, generally found in the Chalinincr, and which I take to 

 indicate periods of growth. With regard to the other species, after the exclusion of oleracea and 

 carotta, for which species Schmidt established the genus Rhizochalina, another name must be chosen, 

 and here Carter's name Plilceodictyon ought to be used, which I ha\-e adopted accordingly. 



