KEPORT ON THE TETRACTINELLIDA. 
CXXl 
With this simplification proceeds a diminution in the size of the desma, so that in the 
Rhabdosa and in the Anoplia it is much smaller than in most of the Trisenosa. In the 
Anoplia ectosomal spicules have disappeared, but the desma is still rhabdocrepid in the 
Azoricidse ; in the Anomocladidse, however, even the crepis disappears, and we are left 
with a skeleton of acrepid desmas and rhabdi. It is worthy of note that, notwithstanding 
the simplification attained by Vetulina, the only existing Anomocladid, the mass of its 
skeleton as compared to that of the sponge is larger than in any other Lithistid, probably 
larger than in any other known sponge. 
A summary of the foregoing classification and an account of families and genera will 
now be given : — 
Tribe TETRACTINELLIDA, Marshall. 
TetracUnellida, Marsliall, Zeitschr. f. wiss. ZooL, Bd. xxvii. p. 134, 1876. 
Demospongise in which triaene or tetraxon megascleres, or Lithistid desmas, are present. 
These characters fail in a single family, the Placospongidae, with a single genus, 
Placospongia ; this is included in the Tetractinellida on account of the presence of 
sterrasters, which are not known in any other Sponge outside the Tetractinellida. 
Order I. CHORISTIDA, Sollas. 
Choristida, Sollas, Ann. and Mag. Nat. Hist., ser. 5, vol. vi. p. 386, 1880. 
Tetractinellida in which Lithistid desmas are absent, and the megascleres are never 
articulated to form a coherent skeleton. 
Suborder I. SIGMATOPHOEA, Sollas. 
Sigmatophora, Sollas, Article “Sponges,” Encyclopaedia Britannica, vol. xxii. p. 423, 1887. 
Choristida in which the microsclere, when present, is a sigmaspire. 
Family I. T E t i l l i d a:, Sollas. 
Group Tethyina, Carter, Ann. and Mag. Nat. Hist., ser. 4, vol. xvi. p. 67, 1875. 
Tetillidae, Sollas, Sci. Proc. Roy. Dubl. Soc., vol. v. p. 178, 1886. 
Historical. — The earliest described species of Tetillid Sponge is Craniella [Alcyonium) 
cranium, Muller.^ This was subsequently associated by Lamarck with a Monaxonid 
Sponge, Tethya lyncurium, in the same genus Tethya, Lamarck.^ That Tethya cranium 
and Tethya lyncurium are genericaUy different was first recognised by Gray,® on whom 
devolved the responsibility of finding a new name for one of them. Tethya lyncunum 
^ Miiller, Zool. Dan., pi. Ixxxv. fig. 1, 1789. ^ Lamarck, Me'm. d. Mus., t. i. p. 71, 1815. 
3 Gray, Proc. Zool. Soc. Lond., p. 543, 1867. 
(zool. chall. exp. — PART Lxiii. — 1888.) Err q 
