[DAWSON] FOSSIL SPONGES AND OTHER ORGANIC REMAINS 



111 



The oxainples of this Hpecios wore prolmhiy nnirly cyliiidnciil tul»«H 

 from ;{() to 5u mm. in iormth, and about 1*2 mm. in width. Tlie longi- 

 tudinal f'uHcicloH an' altout 1 ;nm. apart and the transvt-rsi' tilires from 1 

 to 2 mm. (li«tant from oach olliei-. The projoclinn; Hpicular rays of tlio 

 BurfacoH are (miy Boon in them* compronsod 8ponfi;o8 at tho lateral marj^ins 

 UH a Hort of fringe. The free rayw are Homowliat thickly set ; they vary 

 fronj 5 mm. to 3 mm. in loni^th ; tlio lon;^«'r formn in somo instanci's occur 

 at rc^^ular inlervalw, prohahly at the angles of the mesh, and between 

 thoise are tlio shorter rays. The extremities of many of the lar^ei" forms 

 are slifxh'ly swollen or club-shaped, but it is uncertain whether this is 

 an oriifinal feature or is due to an irref^ular deposition of the pyrites 

 which has now in all cases replaced the silica. 



This species a{)pears as ribb.'nd-like bands composed of vertical and 

 )»ai'allel bundles of delicate spi^uh^s, with slender transvei-se spicules 

 crossintf them at interval? like the rounds of a ladder. It was ])robably 

 oriu;inally cyliudi'ical, but the extremities have not been seen, though 

 fraifiuents nearly three inches in lenj^th have been ft)und. One of its 

 most conspicuous character is the possession of dense fringes of long 

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

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

 sive s|)icules sprii'g. Scattei-ed cruciform spicides of snuill size appear 

 also in the middle of the bands. The fascicles of longitudint:' ipicules 

 are sometimes loosely twisted in a spiral numnej". Ilinde suggests that 

 in some of our s])onges this appearance nuiy be caubod by the accessory 

 threads, indicated by Schulze as (Jotnitalia} 



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 Aranthodlctya 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 Acanthodictya. This specimen 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 possible tliat some of the spirady 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 

 b)- its cylindrical form, the fascicled character of its longitudinal rods, 

 and its cortical spicular arrangements. 



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



