PORIFERA OF THE L.M.B.C. DISTRICT. 223 



of dark grey colour. In April, 1889, I collected in the 

 same cave several specimens of Seiriola which were white 

 with a slight greyish tint, and have kept their colour per- 

 fectly w^ell in strong spirit. The specimens have ahout 

 the same dimensions as the original one, but they are 

 flatter. Although the shape and colour of this sponge 

 agree completely with those of Stelletta colling si, B., which 

 I collected at the same time and in the same locality, still 

 one may distinguish the two forms in the following way : 

 Stelletta has a hispid surface ; Seiriola is smooth to the 

 touch ; Stelletta shows a cortex even in a rough vertical 

 section made with the pocket-knife ; Seiriola does not. 

 Curiously also a specimen of the new material was en- 

 crusted by Suherites domuncula, and in the same way also 

 one or two specimens of Stelletta colliiu/si. The rest were 

 not encrusted, Oscula and pores were not visible in the 

 living specimens. 



The skeleton of Seiriola compacta consists of megascleres 

 and microscleres. The former show the following forms : 

 dichotriaena, orthotriasna, oxea, styli, strongyla, tylota. 

 The dichotriaena are very numerous, and are arranged im- 

 mediately beneath the surface, with their cladomes directed 

 towards the surface. The rhabdome measures from 0"36 

 to 0*42 mm., the protocladus from 0'06 to 0*09 mm., and 

 the deuterocladus from 0'037 to 0*45 mm. The ortho- 

 triaena are far less numerous and slightly smaller than the 

 dichotriaena. They are also placed close to the surface. 

 The oxea are the most numerous spicules, and are arranged 

 in bundles, which take their origin in or immediately 

 beneath the region of the triaena, and stretch vertically 

 down through the whole depth of the sponge. The oxea 

 measure 0'34 to 1"5 mm. by 0'009 to 0'026 mm. Amongst 

 them we find a few stylote, strongylote, and tylote spicules. 



The microscleres are oxyasters, 0*025 mm. in diameter, 



