156 



GEODIA BREVIANA. 



collection of the Geological Survey of Canada and which was kindly placed at 

 my disposal for examination, has shown that it differs from the type of Geodia 

 (Cydoniuni) mulleri and is identical with the specimen referred to above. 



Shape and size. The specimen is fragmentary, 32 mm. long, 21 mm. broad, 

 and 10 mm. thick. Its surface is now fairly smooth, but the living sponge was 

 probably covered with a spiculc-fur. There are three small groups of circular 

 or oval pores 300-800 /t wide, most of which open freely on the surface. The 

 specimen described by Lambe is a thick-walled cup, 6 cm. high, with a rather 

 small cavity, occupied by a high spicule-fur, which consists of long anaclades 

 and mesoproclades. 



The colour, in spirit, is dirty white on the surface, darker in the interior. 



The superficial part of the body forms a cortex, composed of a very thin 

 outer, dermal layer, a middle sterraster-armour layer 700-900 /< thick, and an 

 inner fibrous layer, which latter is, like the dermal layer, destitute of sterrasters. 

 The thinness of the dermal layer may be due to a post mortem collapse in con- 

 sequence of inchfferent preservation. 



Canal-system. A closer investigation of the wide apertures 300-800 /i in 

 diameter, mentioned above, revealed remnants of pore-sieves in many of them. 

 From this I conclude that, in life, all of them were covered by pore-sieves and 

 that, where the sieves are now missing, they have been lost post mortem. Radial 

 canals of equal width and only very slightly constricted below, at the lower 

 limit of the sterraster-armour layer, lead down from these apertures to the 

 choanosome. Outside the regions occupied by the groups of these wide aper- 

 tures (cortical canals) no open canals and only few pores, about 50 // wide, were 

 observed. I take the latter for the afferents and the large apertures in the groups 

 for the places where, in life, the sieves with the efferent pores were spread out. 



Skeleton. Radial bundles of megascleres traverse the choanosome, and 

 penetrate the cortex. Their distal parts appear to have protruded freely and 

 to have formed a spiculc-fur. Their proximal parts are composed of amphioxes; 

 distally orthotriaenes, anatriaenes, and probably also mesoprotriaenes are added 

 to the amphioxes in the bundles. The cladomes of the orthoplagiotriaenes he 

 partly at, partly a little above, and partly a little below, the lower limit of the 

 sterraster-armour layer, the most distal ones being partly enveloped in sterr- 

 asters. Anatriaene-cladomes are quite numerous below the sterraster-armour 

 layer. In the spicule-preparations a few mesoprotriaenes were found, but I saw 

 none in situ in the sections. Minute amphioxes and anaclades are implanted 

 in the distal part of the sterraster-armour. These spicules are situated radially 



