ON FOSSIL SPONGES FEOM METIS. 



49 



au original feature or is due to an irregular de]30sition of the f)yrites which has now in 

 all cases replaced the silica. 



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

 of delicate spicules with slender transverse spicules crossing them at intervals like the 

 rounds of a ladder. It was probably originally cylindrical, but the extremities have not 

 been seen, though fragments nearly three inches in length have been found. One of its 

 most conspicuous characters 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 cruci- 

 form spicules from which the defensive spicules spring. Scattered cruciform spicules of 

 small size appear also in the middle of the bauds. The fascicles of longitudinal si^icules 

 are sometimes loosely twisted in a spiral manner, and it is probable that the root-fibres 

 were spiral. 



Sponges of the above species are sometimes associated with the larger masses of 

 Protospongia in such a manner as to suggest a parasitic or commensal relation, but this 

 may be accidental, and may arise from the cortical spicules of Acanthodictya becoming 

 entangled with the surface of neighbouring sponges. 



It is possible that some of the spirally twisted anchoring rods mentioned below 

 may have belonged to this species, but its root spicules have not been seen attached. 



The genus no doubt approaches to Cyathospougia, but is separated by its cylindrical 

 form, the fascicled character of its longitudinal rods, and its cortical spicular arrangements. 



Genus HYALOSTELIA, Hinde. 



9. — Hyalostelia Metissica, S.N. 

 (Fig. 20.) 



Fig. î-'O. — Hyalostelia Metisgica. Spicules x 5, and large 

 spiral anchoriug rod magnified. 



This species has not yet been seen in a perfect state or showing its general form. It 

 seems to have been of a specially friable or decomposable character. The body appears 

 as irregular patches of broken up skeleton, which, under the lens show a confused mass 

 of cruciform spicules large and small, slender rods and some peculiar triradiate s]3icules, 

 apparently in some cases with oblique angles, though this may perhaps be a result 



Sec. IV, 1889. 7. 



