118 THE SPONGES. 



HALICHONDRINA Vosmaer. 

 HAPLOSCLERIDAE Topsent. 



Petrosia Vosmaer. 



1887. Petrosia Vosmaer, 1887, p. 338. 

 1887. " Vosmaer, Ridley & Deudy, 1887, p. 9. 

 1894. " " Topsent, 1894 a, p. 8. 



1902. " " Luudbeck, 1902, p. 54. 



Petrosia variabilis (Ridley). 



1884. Schmidtia vuriabilis Ridley, 1884, p. 415, Pis. XXXIX., XLI. 



1887- Petrosia variabilis Ridley var., Ridley & Dendy, 1887, p. 13, PI. II., Fig. 12. 



1892. Petrosia variabilis Ridley, Topsent, 1892, p. 68. 



1901. " " " Topsent, 1901 a, p. 11, PI. IL, Kg. 9. 



Petrosia variabilis crassa, subsp. uov. 



Plate 17, Figs. 6, 9, 13; Plate 31, Figs. 3. 3. 



Diagnosis. Form variable, subcylindrical, aud branching, or more or less plate-like and 

 partially incrusting. Body stony ; interior dense. Surface smooth to the eye. Oscula, 

 0.7 to 1.0 mm. in diameter ; rather numerous and scattered. Pores in the meshes of the 

 dermal skeleton, one to a few in the mesh. Oxea, 510 /x x 32 /x. Spiculo-fibres of the 

 main skeletal reticulum 300-600 /i thick, consisting of many rows of spicules ; superficial 

 spicules of the fibre only loosely combined with the body of the fibre ; meshes rounded 

 and of a diameter about equal to thickness of the fibres. Dermal reticulum merely the 

 outermost part of main skeleton, and not differing essentially from it. 



Statmi SJfi5, four specimens. 



Two of the specimens are subcylindrical sponges broken off below (Fig. 9, 

 Plate 17), branching above, the branches rounded off at the free ends. 

 The two specimens are much alike, save that in one the elsewhere solid 

 body is excavated for a length of 35 mm. in its lower part by an axial 

 cavity, which has probably been bored out by the crustacean found therein. 

 In the specimen figured, the length is 60 mm., diameter at the lower end 

 10 mm. 



The other two specimens are of a very different habitus. One is an 

 undulating plate which was obviously attached over a part, at any rate, of 

 its smooth lower surface. The plate has a greatest length of 45 mm. and 

 greatest thickness of 5 mm., thinning away toward the edges. The 

 second specimen (Fig. 12, Plate 17) starts from a similar plate-like ex- 

 pansion, with a smooth imder-surface. It then becomes incrusting upon 

 the branching cylindrical skeleton of an alcyonarian, creeping over the 



