112 



ROYAL SOCIETY OF CANADA 



Genus PAL.EOSACCUS Minde. 

 (Ltmdon Geological ]\r:igazine, Febniîirv. 1803.) 



Cylindrical globular or ^ac-like sponges, with thin walls of i-hombic 

 meshes. The strands of the mesh-work con.sist of fascicles of slender rods, 

 cruciform, and. iierliaj).-^. tive-rayed spicules ; the inters])aces are either 

 open or covered with a thin layer of irregularly disposed rods and cruci- 

 form spicules. No anchoring spicules have been found in immediate 

 connection with the sponge, but there are with it on the same surfaces 

 elongated anchoring-spicules with ornamented spii-al ridges which may 

 belong to it.^ 



From Cyathophycus, Walcott, Avhich appears to be nearest allied, this 

 genus is distinguished by the rhombic character and large size of the 

 mesh- work ; the generally similar structure both of the longitudinal and 

 transverse strands of the mesh, and the greater development of rod-like 

 spicules. The same features likewise ditferentiate it from Plectoderma, 

 Ilinde, and Fhormosella, Hinde. 



10. — Pal.eosaccus Dawsoni, Ilinde. 

 (Figs. 22 and 23. PI. III., Fig. 9, PL IV.) 



Fic. 22.— Spiral ancliorinji-rods, 

 distal ends enlarged. 



Fig. 23.— Portion of anchoring- 

 rod.s, enlarged 



Sjionge of large size, apparently cylindrical in its complete form ; 

 the part preserved consists of a fattened portion of the wall-surface more 

 than a fo.jt in diameter; both the u])per and the I'asal portions of the 

 sponge are wanting. The rhombic meshes of the wall vary from 14 to 

 20 mm. in width, the average width is nearly 17 mm. The strands of 

 the ïnesh mostly consist of very slender rod-like threads a^^pai-ently 

 simple, which ai-e looselj' arranged, in strands of five or more, generally 

 parallel with each other. At the angles of the mesh thei-e are, very 

 frequentiv. if not in all cases, stouter cruciform, or perhaps tive-rayed 



^ Tva/.ain-, ancient ; oaKKor, coarse cloth, sack, strainer. 



