EEPORT ON THE TETEACTINELLIDA. 
227 
and so short that they may more properly be regarded as prosopyles ; their communi- 
cation with the excurrent canals is by means of aphodi, which are about 0‘012 mm. in 
diameter where they enter the chamber. . Their length is variable, standing in adaptation 
to the distance of the chambers from the excurrent canal ; they are either simple or 
unite together branch-like as they approach their termination. 
The choanocytes are preserved chiefly in an extended state ; they measure about 
0‘014 mm. in length. 
The species most nearly related to this appears to be Cydonium glohostellata, Carter, 
which is distinguished by the substitution of orthotrisenes for dichotrisenes, and these are 
smaller than the dichotrisenes of Cydonium eosaster. 
Genus 6. Synops, Vosmaer. 
Poriferous and oscular surfaces of the sponge distinct. Oscules the single openings 
of excurrent chones ; pores in sieves overlying incurrent chones. 
Synops neptuni, Sollas (Pis. XXIV.-XXVI.). 
Synops neptuni, Sollas, Prelim. Account, Sci. Proc. Eoy. Dubl. Soc., vol. v. p. 198, 1886. 
Sponge (Pis. XXIV., XXV.; PI. XXVI. flg. 1). — Cup-shaped; walls thick, diminishing 
to a narrow edge at the summit, attached, sessile. Both inner and outer surfaces deeply 
corrugated, on the outer surface the sinuses of the corrugations continued into the 
thickness of the walls as irregular canals. Surface smooth. Oscules scattered over the 
interior of the cup, pores on the outside. Cortex moderately thick, constituted chiefly 
by sterrasters ; beneath the epithelium a layer of minute chiasters. 
Spicules. — I. Megascleres. 1. Oxea (PI. XXVI. figs. 2, 3), fusiform, straight or curved 
or sinuous, bluntly or sharply pointed, or rounded ofl* at the ends, 1'27 by 0'0193 mm. 
2. Orthotrisene (PI. XXVL fig. 4), rhabdome conical, tapering to a filiform, sharply 
pointed extremity ; cladi curving outwards and but slightly forwards, ends usually 
rounded off or bluntly pointed. Ehabdome 0’964 by O'OIG mm., cladi 0T8 mm. long, 
chord 0’355. 
3. Anatriwne; but a single specimen seen ; cladi short, 0’019 mm. long; rhabdome 
broken, over 0'26 mm. long by O'Oll mm. in diameter. 
II. Microscleres. 4. Sterraster (PI. XXVL figs. 5, 8), spherical, ends of actines 
small, polygonal, bearing five or six recurved spines, 0*448 in diameter. 
5. Somal chiaster (PI. XXVL fig. 10), centrum scarcely distinguishable, several short, 
abruptly truncated, rod-like actines; total diameter when occurring in the cortex 0*006 
mm.; in the choanosome 0*008 mm. 
