130 MARINE FISHES AND INVERTEBRATES OF ST. HELENA. [Jail. 18, 



demonstrate the presence of prosodi *. My own sections also 

 show the prosodi and aphodi. One would expect a priori that 

 in highly developed canal systems with aphodi, prosodi also 

 would, in some cases, tend to arise. For the same development of 

 the choanosome which would lead to the formation of minute 

 excurrent canals lined with epithelium, would lead also to the 

 canalisation of terminal parts of the incurrent system and to 

 their continuity with the pores in the walls of the flagellated 

 chambers. 



The flagellated chambers are spheroidal or pear-shaped, and 

 about 30 x 24 jtx in their longer and shorter diameters respectively. 

 The aphodi open either directly into an excurrent canal or join 

 with one or more aphodi. 



The excurrent canals closely surrounded by dense masses 

 of flagellated chambers appear dark by contrast with the larger 

 incurrent canals surrounded by the " bristle " canals and loose 

 tissue. 



From the above account it will be seen that there are six 

 distinct systems in the total canal system of Chondrosia plebeja, 

 viz. : — (1) the initial pore canals ; (2) the larger incurrent canals ; 

 (3) the radiating " bristle" canals terminating in prosodi ; (4) the 

 cordon of flagellated chambers ; (5) the aphodi ; and (6) the 

 larger excurrent canals terminating in oscules. 



Pigment-cells occur but are not abundant ; thesocytes are 

 numerous. Along the walls of the incurrent canals are the cells 

 of what seems to be a unicellular alga. 



There appear to be five or possibly six known good species of 

 Chondrosia, viz.: — 



C. reniformis Nardo. 



C. plebeja 0. Schmidt. 



C. ramsayi Lendenfeld (? C. reniformis). 



C. debilis Thiele. 



C. corticata Thiele. 



C. reticulata Carter, 



C. collectrix Lendenfeld is, as Topsent surmised, a synonym of 

 C. reticulata Carter, of which latter species C. spurca Carter is 

 also a synonjau. 



Distribution of C. plebeja : — Algiers ; off Porto Santo Island 

 facing the Atlantic coast of Morocco, 60 fathoms (Kirkpatrick 

 coll.) ; Grand Canary, on rocks at low tide (Topsent) ; St. Helena, 

 30 fathoms (Cunningham). 



Specimens from Christmas Island, which I had named C. plebeja 

 (P. Z. S. Lond. 1900, p. 129), belong to C. corticata Thiele. 



* F. E. Schulze, " Uber diplodale Spongienkamnieni," Sitzungsb. Akad. Wiss. 

 Berlin, 1896, ii. p. 891. 



