SPONMIDA. 477 



Of the two species assigned by Mr. Carter (I.e.) to the genus, 

 S. simplex, recorded from Freemantle, Australia, and Hayti, is the 

 most closely allied to the present, but differs from it in the pos- 

 session of the bacillar tuberculate flesh-spicule. Mr. Carter, how- 

 ever, described in the same paper as that in which he founded 

 Stellettinopsis {torn. cit. p. 344), a species which even more nearly 

 approaches the present : this is Amorphina stelUfera from South 

 Australia, which differs from the present form only in its amor- 

 phous, non-pedicellate growth and the proportions of its spicules, 

 which I now give, reduced to metric measurements : — 



1. Acetate, "7 by "017 millim. 



2. Stellate (stated to have no central inflation ; that in S. carteri 

 is hardly worth the name), •017 millim. in diameter. 



Thus the acerate is one fourth and the stellate two thirds smaller 

 than in our species, and hence the two species are, in my view, suffi- 

 ciently distinct. Amorphina stellifera should, however, stand as 

 Stellettinopsis stellifera. 



TETHYOPSIS. 



Stewart, Quart. Jmrn. Micr. Sci. n. s. x. (1870) p. 281 (nee 2^ttel, 

 Abh. layer. Ah. xiii., ii. (1879) p. 9). 



To this remarkable genus I propose to assign a species which 

 has, as described recent allies, the species T. columnifera, from the Phi- 

 lippine Islands, on which the genus was based, and TribracMon (um) 

 sehmidti, from the Gulf of Mexico. Like the latter, the present 

 form exhibits a singular divergence from the more normal Tetrac- 

 tineUid types, in that its chief spicule has lost one of its arms, and 

 is only triactineUid. The genus appears to be allied to Stelletta, 

 the peculiar development of its large tetraotineUid spicule being 

 apparently caused by the erect growth and non-corticate character 

 of the sponge. 



105. Tethyopsis dissimilis. 

 (PiATE XL. fig. H ; Plate XLIII. figs, l-l"""".) 



Sponge elongated, slender, cylindrical or suboblong, tapering 

 to the free extremity, which is pointed ; attached by a narrow base 

 which throws out a thin horizontal expansion outside the sponge 

 itself. Plexible ; surface formed by a thin and delicate dermal, mem- 

 brane of a dark grey colour in spirit. Vent ? Pores •04^-08 in 

 diameter, crowded in the interfascicular spaces of the dermis. 

 Skeleton formed by a number of narrow bands of aggregated spicule- 

 shafts (spicule No. 1) running longitudinally down the interior of the 

 sponge; the bands are united laterally (see fig. V") by means of the 

 arms of the triradiate spicule, are clothed with the soft tissues, 

 and serve to break up the space within the sponge into 8 or 9 

 elongated cavities running from the base towards the apex of the 

 sponge, viz. (1) anterior, (2) posterior, (3 and 4) lateral, (5 and 6) 

 antero-lateral, (7 and 8) postero-lateral, and in one case (9) axial (see 

 figs. I and V). Subdermal skeleton formed by similar longitudinal 



