SPONGES. 83 



Family: GEODIIDJ'.. 



Astrophora, in which the characteristic microsclere is a sterraster, funning a dense 

 cortical layer. 



Geodia, Lamarck. 

 Geodiidse, in which the somal microsclere is a polyactinose aster. 



Geodia perarinata, Bowekbank. 



1873, Geodia perarmatus, BOWERRANK (22); 1880, Geodia perarmata, CARTER (4); 188S, 

 Geodia perarmata, Sollas (15). 



There is an interesting series of specimens belonging to this species in the collection. 

 The smallest is only 13 millims. in diameter, and is approximately spherical in shape; 

 unfortunately, the surface of this specimen is considerably abraded, and I have not 

 been able to make out the arrangement of either inhalant or exhalant apertures. 

 The next in size, about 18 millims. in diameter, is also too much injured to show the 

 arrangement of the apertures satisfactorily. The next is more irregular in shape, 

 about 28 millims. in diameter, and flattened on one side so as to form an approxi- 

 mately circular oscular area about 14 millims. in diameter, but not definitely bounded. 

 This area is covered by a pore-bearing, cribriform membrane, with pores about 

 - 08 millim. in diameter, and few, if any, larger apertures. The remainder of the 

 surface of the sponge, outside the oscular area, is covered with a cribriform dermal 

 membrane containing thickly scattered inhalant pores of somewhat smaller diameter 

 than the exhalant pores. The specimen next in size is also irregular in shape, closely 

 resembling a potato, and about 45 millims. in diameter. The oscular area now forms 

 an ill-defined, but rather deep concavity on one side, whose floor is covered, as before, 

 by a cribriform membrane, hut with a few larger openings where the pores have 

 ajiparently become confluent and thus formed small " vents" ; the maximum diameter 

 of this basin-shaped oscular area, which is not quite circular, is about 17 millims. 

 The largest specimen is a very fine one, irregularly rounded in shape, and about 

 75 millims. in greatest diameter ; it has been attached below at only a few points to 

 calcareous debris. The depressed oscular area occupies the greater part of the 

 flattened upper surface of the sponge, and is about 38 millims. in greatest diameter, 

 and irregularly oval in shape. The floor of the depression is somewhat flattened, but 

 rises up in the middle; the margin is much better defined than in the smaller 

 specimens, but rounded off, except on one side, where it actually overhangs slightly. 

 The pore-bearing membrane presents the same appearance as in the last-described 

 specimen, but the small " vents," due to confluence of the pores, are more numerous ; 

 they are hardly 0'5 millim. in diameter. As before, the general surface of the sponge 

 is covered by a richly porous cribriform membrane. There is also in the collection an 

 irregularly-shaped sub-cylindrical specimen, about 36 millims. in length and 

 18 millims. in diameter, which does not show any distinct oscular area. 



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