REPORT ON THE TETRACTINELLIDA. 
409 
INCEET^ SEDIS. 
Corallistes (f) borealis, Carter. 
CoralUstes borealis, Carter, Ann. and Mag. Nat. Hist., ser. 4, vol. xii. pp. 439, 442, 443, 1873. 
Si^onge (?). — (Overgrown by other sponges.) 
Spicules. — Desmas like those of Azorica pfeifferae. Dichotrisenes and disco- 
trisenes are said to occur in the midst of the skeleton. 
Habitat. — Fseroe Islands. 
Remarks. — The presence of dichotrisenes and discotrisenes in the interior of the 
desmose skeleton is so unique that one is led to suspect some source of error ; disco- 
trisenes are essentially ectosomal spicules, and when they are found in the middle of 
a sponge, they may be looked upon as foreign inclusions. 
Arabescula parasitica, Carter. 
Ardbeseula parasitica, Carter, Ann. and Mag. Nat. Hist., ser. 4, vol. xii. p. 464, pL xvii. 
figs. 7-9, 1873. 
„ ,, Zittel, Abliandl. d. k. baier. Akad. d. Wiss., Bd. i. pp. 103, 120, pi. i. 
fig. 11, 1878. 
Corallistes parasitica, Ridley, Ann. and Mag. Nat. Hist., ser. 5, vol. xiv. p. 183, 1884. 
Sponge. — Thin, incrusting. 
Spicules. — Megasclere. Desma, epirabd, curved, branched, breaking up into 
filagree, depressed in a plane parallel to the surface, smooth externally, with cylindrical 
tubercles on the inner face. 
Habitat. — West of the English Channel, growing over Aplirocallistes bocagei. 
Seychelles, growing over Farrea occa. 
Remarks. — In the specimen which Mr. Carter kindly presented to me, the desmas 
are to be seen as a single layer closely incrusting part of the deciduous skeleton of 
Aphrocallistes bocagei, they much resemble the ectosomal desmas of SipJionidium, but 
probably owe their form to their mode of growth and position, for in the case of 
attached Lithistids the desmas immediately in contact with the surface of attachment 
are frequently flattened in conformity with it, and then in some cases much resemble 
the desmas of Arabescula. As none but the incrusting desmas have been observed in 
this sponge, and nothing is known as to the presence or absence of microscleres, its 
position is eminently doubtful. I do not think it is referable to Corallistes as Ridley 
conceives, but more probably to some genus of the Azoricidse, of which possibly it 
represents only the layer of desmas serving for attachment. 
(ZOOL. CHALL. EXP. — PART LXIII. — 1888.) 
Rn’ 52 
