GEODIA LOPHOTRIAENA. 



181 



the choanosomal rhabds are not, as usual, for the most part amphioxcs, but, as 

 in Geodia amphistrongyla for the most part amphistrongyles, is Sidonops (Geodia) 

 flemin.gii (Bowerbank)/ This species resembles Geodia amphistrongyla not 

 only in respect to the rhabds and sterrasters, but also in respect to the euasters. 

 Since, however, in Geodia amphistrongyla the plagioclades (orthoclades) are simple 

 triaenes and the anatriaene-cladomes very small, while in Sidonops (Geodia) 

 fleviingii the former are dichotriaenes and the latter quite large; since there 

 appears to be a difference in the efferent pores which necessitates the placing 

 of the two in two distinct genera; and since the one comes from the south coast 

 of Australia and the other from Easter Island, there can, I think, be no doubt 

 that they should be kept specifically distinct. 



I establish this species for seven spirit specimens which came probably 

 from New Zealand. They possess, besides ordinary dichotriaenes, a good many 

 lophotriaenes with more than two end clades on one or two or all three main 

 clades and to this the name refers. 



The seven specimens are all cushion shaped and cut off from the surface 

 on which they grew and to which they appear to have been attached by broad 

 bases. Their upper surface is convex, their contour irregularly circular, 

 rounded polygonal, or elongated. The smallest of them is 7 mm. long, 6 mm. 

 broad, and 2.5 mm. high; the largest, which is penetrated in the middle (Plate 

 47, fig. 22), 15.5 mm. long, 11 mm. broad, and 3 mm. high. The surface is 

 entirely destitute of a spicule-fur and appears, when viewed with a lens, 

 shagreened. It is quite continuous, neither depressions nor apertures, visible 

 with the unaided eye, occur in it. 



The colour, in spirit, is brownish, lighter on the surface than in the interior. 



The superficial part of the body is differentiated to form a cortex (Plate 47, 

 fig. 24a), in which an outer dermal layer (Plate 47, fig. 23a), free from 

 sterrasters, rich in sphaerasters, and 30-65 pt thick, and an inner sterraster- 

 armour layer (Plate 47, fig. 23b) 60-125 thick, can be distinguished. 



The cortex is penetrated by numerous radial canals which are 150-250 /« 

 apart. Those observed were strongly contracted, only 5-15 /t wide. These 



' J . S. Bowerbank. Contributions to a general history of the iSpongiadae. IV. Proc. Zool. soc. 

 London, 1873, p. 3, pi. 1, figs. 1-8. W.J.Sollas. Tetractinellida. Ropt. voy. "Cliullcnger ", 1888, 25, 

 p. 252. 



Plate 47, figs. 9-36; Plate 48, figs. 1-34. 



