178 Mr. H. J. Carter on new Species of Subspherous Sponges. 
keeps all the elements of the surface in proper position, coin- 
cide strictly with what has been stated and figured of Tethya 
cranium (Johnston, Hist. Brit. Spong. pl. 1. figs. 1 &c.) and of 
T. arabica ( Annals, 1869, vol. iv. pl. 1. figs. 1 &c.). 
The sigmoid spicules, too, evidently exist in both these 
species of Tethya, in a minuter form (Bowerbank, Brit. Spong. ` 
vol. ii. p. 85, and Annals, /. c.), but being so much larger in 
T. atro-purpurea, where they can be easily seen in detail with 
uarter-of-an-inch compound power, are thus much more 
satisfactorily illustrated. 
I could not discover any gemmules. 
Besides being sessile, this species might occasionally exist 
in a subspherous form, free and unattached, like T. arabica, 
as I know from actual experience such to be the habit of 
these Tethyæ. But the specimen under description appears to 
have been cut off from the rock or object on which it grew, and 
that, too, a little above its real base, as there is no nucleus 
present in the latter, nor any point indicative of the centre 
om which the mass emanated; probably this was left upon 
e rock. 
TRACHYA, nov. gen., mihi. 
Gen..char. Asperous, massive, cake-shaped, free or fixed, 
dense, rigid. Osculiferous. Internally multinucleate. Spi- 
cules of two kinds only, viz. large and small: large spicule 
smooth, fusiform-acerate; small spicule, which is chiefly 
confined to the upper surface, smooth, fusiform-acuate. 
Trachya pernucleata, n. sp. mihi. Pl. XIII. figs. 11-16. 
with the spicules lying on or inclined towards the su in 
flattened whorls or radiated groups (fig. 15), not projecting 
vertically, as on the upper surface (fig. 13). ally com- 
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