REPOET ON THE TETEACTINELLIDA. 
CXXIX 
owing to the lateral position of both oscule and poriferous recess, which are of nearly 
equal size and situated on opposite sides of the Sponge. 
As a rule radical fibres descend from the base of the Sponge and either end separately 
in splayed out leashes, or become matted together into a basal mass. 
The spicules usually include the following : — 
I. Megascleres — (1) oxea ; (2) protrisene or plagiotrisene ; (3) dichotrisene with very 
long deuterocladi ; (4) anatrisene, which may be differentiated into a somal and radical 
form. 
II. Microscleres — (l) spiraster, or amphiaster; (2) metaster, and (3) plesiaster or 
oxyaster. 
Although the mesoderm is always collenchymatous, it is very variable in quantity, 
sometimes being reduced to a minimum, so that the folding of the choanosomal plate is 
obvious, sometimes on the other hand increasing to so great an extent that no suggestion 
of the origin of the canal-system by folding is discernible, the canals being provided with 
thick collenchymatous walls, and vela occurring at intervals no further apart than the 
diameter of the canal, which is thus converted into a succession of vesicles. Reproduction 
is both sexual and asexual (by external gemmation). 
Genus 2. Characella, Sollas. 
Characella, Sollas, ScL Proc. Hoy. Dubl. Soc., vol. v. p. 187, 1886. 
Theneidse of irregular form ; oscules and pores not regularly distributed ; megascleres 
not radially arranged, consisting of oxeas and orthotrisenes and dichotrisenes ; the trisenes 
are confined to the ectosome. The microscleres are microxeas and amphiasters. The 
mesoderm is a collenchyma, containing numerous granules. 
Type — Characella aspera, n. sp. 
This genus is closely allied to Pcecillastra, from which it differs by the absence of 
trisenes from the choanosome. The character of the mesoderm may furnish another 
point of distinction. 
Genus 3. Pcecillastra, n. n. 
Normania, Bwk., Norman, Brit. Assoc. Report, p. 328, 1868. 
„ Bowerbauk, Mon. Brit. Spong., vol. iii. p. 258, 1874. 
„ Sollas, Sci. Proc. Roy. Dubl. Soc., vol. v. p. 185, 1886. 
Theneidse without special symmetry, but usually of plate-like form, bearing on one 
surface the oscules and on the opposite the pores, which are never collected into special 
recesses. The skeleton consists of oxeas, tritenes, and calthrops, which are aggregated 
into more or less longitudinal and transverse bundles or indistinct fibres, the trisenes 
(ZOOL. CHALL. EXP. — PART LXIII. — 1888.) Err r 
