REPOET ON THE TETRACTINELLIDA. 
45 
differences. The hispidating spicules are represented as all directed downwards, and the 
base of anchoring fibres are much larger in proportion to the sponge, and apparently 
denser than in my specimen. Measurements obtained from Carter’s description and 
illustrations of the spicules of the type exceed those obtained from the Mergui specimen, 
which is characterised by the comparative smallness of its spicules ; though small 
they are remarkably numerous, as if in compensation, and both by their abundance and 
smallness give quite a distinctive facies to the sponge. The ectosome is thin ; the 
choanosome is crowded with flagellated chambers, lying so close together as to reduce to 
a minimum the mesoderm, they measure about 0’04 by 0’032 mm. ; the choanocytes are 
free (^.e,, not confluent by their collars), with long flagella. Although my observations 
were not altogether satisfactory, I came to the conclusion that the chambers are eury- 
pylous, but the common canal into which they open is so small in most cases, that the 
nature of the communication is generally somewhat obscure. About the oscule the 
mesoderm is developed to the exclusion of flagellated chambers, it there forms a tissue 
consisting of oval, granular, not very deeply stained cells, set near together in a matrix 
which stains more deeply than the cells themselves. 
Tetilla euplocamus, 0. Schmidt. . 
Tetilla euplocamus, 0. Schmidt, Spong. Algiers, p. 40, pi. v. fig. 10, 1868; Atlant. Spong. 
Gebiet., p. 66, 1870. 
„ „ (1) E. Selenka, Zeitschr. f. wiss. ZooL, Bd. xxxiii. p, 469, 1880. 
Sponge small, pear-shaped; surface pilose; rootlets formed of spirally twisted 
anchors. 
Spicules. — I, Megascleres. Oxea, fusiform, 2 '3 by 0*22 mm.; trichodal protrisenes 
(and anatrisenes ?). 
II. Microscleres (?). 
Habitat. — Desterro, South Atlantic (0. Schmidt). Western part of the Bay of Eio 
de Janeiro ; depth, exposed at lowest spring- tides ; bottom, sandy mud (Selenka). 
Remarks. — No one from Schmidt’s meagre description of this species could hope to 
identify it, unless by means of the spiral twist of the anchoring filaments, and this, very 
possibly, is not characteristic. A slide of mounted spicules, presented by Schmidt to 
the British Museum, showed oxeas of Tetilla-Wke, form, and trichodal triaenes, but no 
anatrisenes nor sigmaspires. Selenka, with great probability, assigns a small Tetilla 
which he found at Eio to this species ; it is of an olive-green to yellowish-brown colour ; 
and is found at lowest ebb-tide, with the roots completely immersed in the sandy 
mud of the sea-floor, and the body projecting above. Tetilla euplocamus is most readily 
distinguished from Tetilla leptoderma [vide p. 3) by the smaller size of its oxeate 
spicules, which are only half the length and breadth of those in the latter species. 
