SPONGES. 273 



vertical series. Portions of the more or less tortuous vertical 

 canals also may be presented to view. Generally, however, the 

 sides present a very irregular network of canals. 



Height of largest example varying between 18 and 40 mm.; 

 greatest width about 90 mm. 



The three specimens of this species contained in the collection 

 before us, are in too poor a state of preservation to admit of 

 satisfactorily determining all the details. One of them is very 

 det-Hptive. as it is attached to the lower surface of a species of 

 Anthaspidella and has adapted itself so neatly to it that the 

 osculiferous face was supposed to belong to the Edriospongia. 

 This mistake was not discovered till some time after the speci- 

 men had been lithographed (PI. VI, fig. 1, la) and the plate 

 printed. It then occurred to us to saw the perplexing specimen 

 vertically through the centre. When this was accomplished the 

 duplex character was made manifest, as the section clearly 

 shows a divisional line between the two sponges. Another diffi- 

 culty, now presented, was to determine whether the Edriospongia 

 had grown upon the Anthaspidella, or the former been accidentally- 

 deposited upon the upper surface of the latter. All the facts 

 seem to point to the second explanation as the true one. Every 

 character of the lower surface of the specimen as it is repre- 

 sented by fig. la, brings evidence against the conclusion that 

 we are dealing with the upper surface of the sponge, but on 

 the contrary, agrees in every respect with our idea of the base 

 of a parasitic sponge. It therefore appears that during the 

 lifetime of the Edriospongia the Anthaspidella was deposited 

 upon its upper surface, without seriously interfering with the 

 functions till the gradual increase of the sponge mass had 

 stopped the water circulation by closing the canal outlets. 



Position and locality: Twenty-five feet above the base of the 

 Trenton limestone, near Dixon. Illinois. 



STREPTOSOLEX nov. gen. 



Sponges simple or compound, obconical, pedunculate. Central 

 oscula showing the mouths of five or six thin walled tubes, 

 which extend'through the sponge to the base. The oscula are 

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