THE PORIFERA. 89 



Dercitus niger.-' This is the sponge which Dr. Bowerbank 

 likened in appearance to a piece of bullock's liver. 



Mr. Carter has included it in his family Pachastrellida, 

 which embraces Schmidt's genus Pachastrella, and the 

 Lithistid, or stony sponges. 



L. F. M., No. 4. 9. 74, 4. Collected at Holyhead. 



Order VIII.— C A LC AREA. 



The only monograph of the Calcarea or sponges which have 

 calcareous spicules is that published by Professor Haeckel f 

 in 1872. Previous and subsequent writers have described a 

 few species only, but Haeckel had a large number before him. 

 There has been a general concurrence in his classification, 

 though exceptions have been taken to some of his views and 

 speculations. The Calcarea of the " Challenger " Expe- 

 dition were examined and reported upon by Dr. N. Pole- 

 jaeiF, I of the University of Odessa, a distinguished pupil of 

 Professor F. E. Scliultze ; and, at the present moment, Mr. 

 H. J. Carter, F.R.S., of Budleigh Salterton, has under 

 examination a very large collection from Australian waters. 

 Dr. Polejaeff had only a few species to report upon. 



Professor Haeckel divided the whole order into three 

 families, Ascones, Leucones, and Sycones, according to the 

 canal system, and these again into groups and genera, 

 according to the prevailing forms of spicules. " The 

 Ascones present the simplest form of the canal system. The 

 thin wall of the sponge consists of three parallel layers, ecto- 

 derm, mesoderm, and endoderm. Here and there the cells 

 separate, and thus give origin to the pores " (Vosmaer.) The 



* Mon. Brit. Spong. vol. ii, p. 226 ; vol. iii, pi. xxxviii, fig. 9-12, and 

 pi. xcii, fig. 8, p. 346. Annals and Mag. Nat. Hist., 1871, vol. vii, p. 3, 

 pi. iv, fig. 1, etc. Proc. Zool. Soc , 1867, p. 542. 



i Die Kalkschicamme, Haeckel, 1872. 



\ Report on the Calcarea, by Dr. N. Polejaeff, M.A., Zool. Cliall. Exp., 

 part xxiv, 1883. 



