REPORT ON THE TETRACTINELLIDA. 
347 
the sponge, and near the larger canals lie tangentially to their walls. The sigmaspires 
occur throughout the sponge. The margins of the sphincters of the oscules and the 
pores are bounded by the microstrongyles of the dermal layer, and the exposed surfaces 
of the sphincters show beneath the epithelium numerous sigmaspires. 
Colour. — (?). Size, 18 mm. in diameter by 12 mm. in height. 
Habitat. — Station 307, Agassiz. 
Remarks. — This sponge is very clearly distinguished from Scleritoderma jlabelli- 
formis from the Ki Islands, partly by the general form, and partly by the size of the 
microstrongyles, which are twice the length of those in the latter species. 
Genus 2. Aciculites, 0. Schmidt. 
Scleritodermidae in which the ectosomal spicules are rhabdi ; microscleres are absent. 
The occurrence of an ectosomal layer of rhabdi suggests an alliance with Sclerito- 
derma; and since, judging from the Tetillidse, the sigmaspire is an inconstant spicule, 
its absence is not a matter of such importance as to exclude the genus from the Sclerito- 
dermidse. 
Aciculites higginsi, 0. Schmidt. 
Aciculites higginsi, 0. Schmidt, Spong. Meerb. Mexico, p. 29, pi. ii. figs. 1, 4, 13, 1879. 
Sponge. — Cushion-shaped, attached either by the entire base or by its margin only; 
in the latter case the middle of the base rises upwards, so as to leave a large hollow cavity 
between it and the surface of attachment. Oscules one or several, seated on the summit 
of slight conical elevations or in slight depressions, forming the centre of a stellate 
system of superficial canals, which can be traced as ramifying dark-coloured lines beneath 
the surface, provided with a sphinctrate margin, protected by a tent-like arrangement of 
rhabdi, which radiate from the circumference towards the centre. Pores simple, 0'03 
mm. in diameter. 
Spicules. — I. Megascleres. 1. Desma, small ; cladi short, thick, richly tuberculate, 
protocladi 0‘06.5 by 0’026 mm. to 0‘084 by 0’039 mm. 2. Rhahdus, variable, usually a 
tylotostrongyle, the tylus scarcely thicker than the rhabdome, minutely spined ; rhab- 
dome smooth, cylindrical, curved ; sometimes a strongyle, sometimes, but very rarely, a 
tylotoxea, 0‘271 by O'Ol mm. to 0'355 by O’Ol mm., but variable, sometimes much 
shorter. 
II. Microscleres absent. 
Beneath the external epithelium the rhabdi form a single layer lying tangentially; 
they also occur directed at right angles to the surface, with the tylus directed outwards 
