50 
THE VOYAGE OF H.M.S. CHALLENGER. 
larger than usual and appear to pass into the microstrongyles, and as these pass from a 
highly curved to an almost straight form, we appear to have here another case of the 
development of a rhabdus from a spire. 
The specimen of the sponge is unfortunately a dried one, and in the absence of any 
exact knowledge of its general anatomy, it is impossible to determine its true place 
among the Tetdlid genera. The cortex appears to be that of Tetilla, but the characters 
of its spicules are so peculiar (probably in adaptation to the stalked manner of attach- 
ment) that one would not be surprised if, on further examination, it were found to be 
the type of a new genus. The amphitrisenes sometimes are reduced to simple trisenes, 
the end of the rhabdome, from which a trisene has disappeared, being then strongylate. 
I was not able to satisfy myself of the independent existence of the anatrisene, it appeared 
to me possible that it might be a form of the amphitrisene. 
Craniella ahyssorum (Carter). 
Tethya cranium, var. ahyssorum, Carter, Ann. and Mag. Nat. Hist., ser. 4, vol. xviii, p. 405, 
pi. xvi. fig. 49, 1875. 
„ ,, „ „ Norman, Bowerbank, Mon. Brit. Spong., voL iv. p. 39, 1879. 
Sponge similar to Craniella cranium. 
Spicules. — I. Megascleres, 1. Somal oxea, 4'3 by 0'045 mm. 2. Cortical oxea, 
0'7 by 0‘045 mm. 3. Protrisene, rhabdome 4'3 by 0'022 mm.; cladi 0‘22 mm. long; 
chord O'll mm. 4. Anatrisene, rhabdome 6*5 by 0‘02 mm.; cladi 0T16 mm. long; 
chord 0T6 mm. 
II. Microsclere. 5. Sigmaspire, 0'02 mm. long. 
Habitat. — Deep-sea, between the north of Scotland and the Fseroe Isles (Carter). 
Remarhs . — The sigmaspire is much larger than in Craniella cranium, and frequently 
forms a little more than one revolution of a spiral; in addition the cladome of the 
anatrisene is characterised by longer, more slender, and more divergent cladi than in 
the corresponding spicule of Craniella cranium; the cortical oxea also is smaller. 
Hence I prefer, while admitting that it is very much a matter of taste, to make Carter’s 
variety a distinct species. 
Craniella atropurpurea (Carter). 
Tethya atropurpurea. Carter, Ann. and Mag. Nat. Hist., vol. vi. p. 176, pi. xiii. figs. 1-10, 1870. 
Sponge spherical, compressed, free ; surface raised into conules. 
Spicules. — I. Megascleres. 1. Somal oxea, 3‘57 by 0'0556 mm. 2. Cortical oxea, 
1‘25 by 0'0556 mm. 3. Protrisene, 5‘0 by 0’014 mm. 4. Anatrisene, rhabdome 5'0 by 
0'014 mm. 
