293 
to our Knowledge of the Spongida. 
inch long by 1-1800th broad, the echinating arm a little 
longer than the rest, sharper, and standing out from the others 
at a greater angle (fig. 6, d , and fig. 7). Nos. 1 and 2 pro¬ 
ject obliquely upwards and outwards from the surface ] no. 3 
is sparsely mixed among them, and no. 4 very plentifully 
distributed about their fixed ends (fig. 8, a, b , c, d). No. 4 
also is often quinqueradiate (fig. 6, e), and as often presents 
itself under the form of three- and four- smooth-armed radiates 
whose rays are sharp-pointed (fig. 6,f g). Size of fragment 
about 1 inch long, in the direction of the radiated structure 
(that is, vertically), and I inch thick. 
Hab. Marine. 
Loc. West Indies. 
Obs. Examined in the dried state. From the dirty and insig¬ 
nificant appearance of this fragment, which appears to repre¬ 
sent the total vertical thickness of the sponge, it is not impro¬ 
bable that, growing on rocks in shallow muddy water in the 
form of a crust with plane and unbranched surface, it has 
often been overlooked. Nevertheless, from the above descrip¬ 
tion, it is evidently very desirable that better specimens of it 
should be obtained; for being one of the Echinonemata in 
which radiate spicules at once like those of Pachastrella and 
those of the Calcispongise are present, it is important that this 
fact should be made public, as the two following sponges are, 
in spiculation, allied to it, and all might be confounded, in the 
fossil state, with the Calcispongise, if the latter were alone 
supposed to contain the triradiate and quadriradiate spicules, 
as Mr. Sollas’s illustrations and descriptions of his fossil 
genus “ Catagma ” show (‘ Annals,’ 1878, vol. ii. p. 353, 
&c.). 
The splitting-up or subdivision of the columnar structure 
towards the surface into lacinulated heads is a common fea¬ 
ture of Dictyocylindrus , but not less characteristic of the sur¬ 
face of many of the Echinonemata, where the projecting 
lacinula may vary in form from flat to round, being fre¬ 
quently spatulate or tongue-shaped with a caudate extremity. 
Trikentrion muricatum , Ehlers, 1870. 
(PI. XXVII. fig. 13.) 
In 1756 Pallas (Elench. Zoophytorum, p. 389. no. 237) 
described this sponge under the name of Spongia muricata , 
stating, on the authority of Seba, that it comes from “Guinea.” 
In 1794 Esper (Die Pflanzenthiere &c. pi. 3) figured and 
described it under the same name from a specimen now in 
the museum at Erlangen, which, after microscopic examina¬ 
tion, Dr. Ehlers, in 1870, considered it desirable to distinguish 
Ann. & Mag. N. Hist. Ser. 5. Vol. iii. v 20 
