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Show 1881.] THE SURVEY OF H.M.S. 'ALERT.' 137 spicules, whose sagittal rays lie between the radial canals, and whose lateral rays serve to enclose them. The cloacal surface is formed of a layer of mingled small and larger quadriradiate spicules. Acerate Spicules. Straight, surface minutely rough, tapering to sharp points from the centre. Average maximum size 2*1 by "095 millim., extending from just beneath the cloacal to about one fourth of their length beyond dermal surface. Stout Triradiates. Sagittal rays straight, surface slightly roughened, tapering to approximately sharp points from the base, forming three angles of about 120° each. Size of rays varying (average maximum size) : basal from "304 by "04434 millim. to '424 by -05067, laterals from "2217 by "038 to "3167 by -04434-the proportion between the lengths of the two being thus 5 : 3 or 4:3. The basal ray is generally parallel to the long axis of the sponge, while one of the laterals projects from the dermal surface. Slender Triradiates. Rays smooth, tapering from base to sharp points ; the basal ray straight, the laterals either straight, or curving slightly forwards, or slightly undulating ; the inwardly facing laterals form an oral angle of from 160° to 180° with each other ; the basal points outwards ; lateral angles equal. Size of rays varying (average maximum size): basal from "38 by "019 millim. to "3167 by "019, laterals from '152 by '0158 to -139 by *158 ; the proportion between the lengths of the rays is therefore 5 : 2 or 7 : 3. Quadriradiates. Rays smooth, tapering from base to sharp points; basal straight, laterals slightly curved, either to or from cloacal surface, forming an oral angle of from 130° to 170°. Apical ray straight, projecting into cloaca. Size of laterals almost constant ; apicals and basals vary inversely in length with each other. Basal ray either about "285 by "019 millim., or "04434 by "0095 ; laterals (average maximum) "0S235 by "0095 to "101 by "01267; apical either "019 or "0507 by "006334. Examined. In spirit and by sections mounted in balsam. Hab. Victoria Bank (off S.E. Brazil), 39 fathoms ; bottom, dead coral. Obs. The species is represented by a single specimen 10 millims. long by 5*5 in extreme breadth. The projection of the points of the acerate and stout triradiate spicules from the surface is disguised to some extent by an aggregation between them of a yellowish material, which appears to be the result of desquamation of the surface tissues. This species resembles Leucandra cyathus, Verrill1, from Casco Bay, U. S., in its spicule-characters, and differs from all the species assigned to Sycandra in the 'Kalkschwamme' of Hackel by the possession of a cortical layer of triradiates with rays at least twice as stout as those of the triradiates forming the main substance of the sponge. 1 Proc. Amer. Assoc. Adv. Science for 1873, p. 392. |