528 ARTHUR DENDY. 



lacuna, to be less primitive than the canalicular type, in which 

 the chambers are provided with special canaliculi. There is 

 not sufficient evidence at present to show whether or not this 

 is the case, but I think it not impossible that it may be so. 



EXPLANATION OF PLATE XLII. 



Illustrating Mr. A. Dendy's paper " Studies on the Com- 

 parative Anatomy of Sponges. I. On the Genera Ridleia, 

 n. gen., and Quasillina, Norman." 



Tigs. 1 — 7. — Ridleia oviformis. 



Fig. 1. Entire Sponge, x 2. o. Osculum. a a. Flattened surfaces, by 

 which'the Sponge has probably been attached to pebbles. 



Fig. 2. Longitudinal section, taken at right angles to the surface shown 

 in Fig. 1, X 5. o. Osculum, leading into oscular tube; the black line 

 indicates the distribution of the fibrous tissue. (The figure is rather dia- 

 grammatic ; the canals radiating towards the centre are exaggerated.) 



Fig. 3. Portion of transverse section, x 44. ect. Ectosome. ch. choano- 

 some. p. Pore, leading into slit-like subdermal cavity, e. e. Exhalant 

 canals converging towards the centre of the Sponge. /./. Layer of 

 longitudinal fibres cut across, c.f. Layer of circular fibres, sp. b. 

 Bundles of small spicules projecting at surface. I. sp. Longitudinal 

 bundles of spicules cut across, i. sp. Oblique fibres of spicules within 

 the choanosome cut across. (A little diagrammatic.) 



Figs. 4 and 5. Two of the larger tylostyli x 190. 



Fig. 6. One of the small tylostyli X 500. 



Fig. 7. Diagram of diplodal canalicular canal system, as it occurs in 

 Ridleia oviformis, X 190. i.e. Inhalant canal, giving off narrow 

 canaliculi to/, c, the flagellated chambers, which communicate again by 

 narrow canaliculi with e. c, an exhalant canal. 



Figs. 8 — 12. — Quasillina brevis. 



Fig. 8. Entire Sponge attached to a pebble, nat. size. (After Ridley and 



Dendy, ' Report on the " Challenger " Monaxonida.') o. Osculum. 

 Fig. 9. Part of longitudinal section passing through the osculum, x 23. 

 o. Osculum. p. Pores, s. c. Subdermal cavities. /. Lacunae of canal 



