[DAWSON] FOSSIL SPONGES AND OTHER ORGANIC REMAINS 111 



The exumplcfi of this species were pi-ohahly iieiirly cylindrical tubes 

 from 30 to 5U mm. in ieng-tli, and ahout 12 mm. in width. The lon<i;i- 

 tudinal fascicles are ahoul 1 mm. a[)ai't and the ti'an.sverse tihi-e.s from 1 

 to 2 mm. distant from each other. The projecting spicular rays of the 

 surfaces are only seen in these compressed sponges at the lateral margins 

 iis a sort of tVinge. The free rays are somewhat thickly set ; they vaiy 

 from 5 mm. to 3 mm. in length ; the longer forms in some instances occur 

 at regular intervals, probably at the angles of the mesh, and between 

 these are the shorter raj^s. The extremities of many of the larger forms 

 are slightly swollen or club-shaped, but it is uncertain whether this is 

 an original feature or is due to an irregular deposition of the pyrites 

 which has now in all cases replaced the silica. 



This species appears as ribband-like bands composed of vertical and 

 parallel Inindlcs of delicate spicules, with slender transverse spicules 

 crossing them at intervals like the rounds of a ladder. It was probably 

 originalh' cylindrical, Init the extremities have not been seen, though 

 fragments nearly three inches in length have l)een found. One of its 

 most conspicuous charactere is the possession of dense fringes of long- 

 protective sjiicules at the sides, and these seem to be based on a cortical 

 structure of crutch-shaped or cruciform spicules, from which the defen- 

 sive spicules spring. Scattered cruciform spicules of snuiU size appear 

 also in the middle of the bands. The fascicles of longitudinal spicules 

 are sometimes loosely twisted in a spiral manner. Hinde suggests that 

 in some of our sponges this appearance may be caused l)y the accessory 

 threads, indicated by Schulze as Comitalia} 



Sponges of the above species are sometimes associated with the 

 larger masses of Protospongia in such manner as to suggest a parasitic 

 or commensal relation ; but this may be accidental, and may arise from 

 the cortical spicules of AcantJiodictya becoming entangled with the sur- 

 face of neighbouring sponges. In one specimen 1 have the anchoring- 

 rods of Protospongia. tetranema, with a patch of pyrite inclosing some 

 of the spicules' at the top and apparently attached to this, and rising 

 from it a specimen of Acanthodlctya. This sjijccimen certainly appears 

 to suggest a commensal relation. Another specimen is attached laterally 

 to the side of a fragment of Protospongia, and another is very long and 

 much curved. 



It is ])ossible that some of the spirally twisted anchoring-rods men- 

 tioned below may have belonged to this species, but these have not been 

 seen attached, and there are only faint indications of simple or loosely 

 spiral roots. 



The genus, no doubt, approaches to Cyathophycus, but is separated 

 by its cylindrical form, the fascicled character of its longitudinal rods, 

 and its cortical spicular arrangements. 



^ Challenger Report, vol. xxi., page 17. 



