THE SPONGES. 127 



arranged imiserially ; in the coarser, in several series up to about 6. 

 There are a few free spicules, all of the smallest size given above, scattered 

 in the meshes of the skeletal reticulum. 



The supporting reticulum of the dermal membrane (Fig. 1, Plate 17) 

 consists of stouter and finer fibres, like those of the main skeleton. Stouter 

 fibres, 40-60 fx thick, form coarse meshes which are subdivided by finer 

 fibres 15-30 fx thick; ultimate meshes squarish or polygonal with diameter 

 150 fM to 350 jx. In the larger fibres the spicules are arranged polyserially 

 (about 10 rows) ; in the finer fibres uniserially or in two to a few rows. 

 From coarse and fine fibres alike project abundant villi, many of them 

 about 120 jx high and consisting of a bunch of spicules, 4 or 5 spicules 

 thick, with considerable horny matter; others consisting of only 2 or 3 

 spicules. Some of the villi are prolongations of radial skeletal fibres ; 

 others are independent projections from the dermal reticulum. 



Comparative. The species above described resembles in the lamellate 

 character of its growth, and in some other respects as well, Pachychalina 

 spinilamella Dendy (Dendy, 1889), a type specimen of which I have ex- 

 amined. The lamellate character, which is disguised in P. acapukensis, is 

 pronounced in Dendy's. The spicules in P. spinilamella are exceedingly 

 slender, measuring about 0.126 by 0.0017 mm. 



Oceanapia Norman. 



1869. Oceanapia Norman, Rep. Brit. Ass., 1868 (1869), pp. 334-35 (generic diagnosis here given is 

 quoted in Bowerbank, 1882, p. 171). 



1870. Rhizochalina O. Schmidt, 1870, p. 35. 

 1882. mioeodictyina Carter, 1882, p. 117. 

 1884. Rhizochalina Schmidt, Ridley, 1884. 



1887- Rhizochalina Schmidt + Oceanapia Norman, Ridley & Dendy, 1887, pp- 32, 36. 



1894. Oceanapia Norman, Dendy, 1894, p. 248. 



1894. Rhizochalina Schmidt + Oceanapia Norman, Topseut, 1894 a, p. 10. 



1902. Rhloeodictyon Carter + Rhizochalina Schm. + Oceanapia Norman, Lundbeck, 1902, pp. 55-56. 



Ridley (1884) merged Pliloeodictyon Carter in Rlmochalina Schmidt. 

 Ridley and Dendy (1887, p. 32) suggest that Rhizochalina (+ PhloeodicUjon) 

 and Oceanapia Norman should be united, and Dendy (1894) combines the 

 two under Oceanapia, while Topsent (1894 a) retains the separate genera. 

 Lundbeck (1902) thinks that the group Phloeodictyina (= Oceanapm^ sensu 

 Dendy) includes three separate genera, Rhizochalina Schm., Phlocodictfjon 



