A FOSSIL BUREnWIXG SPOXOE FROM THE IOWA 

 DEYONIAX 



BY A. O. THOMAS. 



Cliona liackherryensis. nov. sp. 

 Plate 



Burrows tubular and of uniform size being from two to three 

 tenths of a millimeter in diameter ; usually found penetrating the 

 sheUs of brachipods especially those of Orthis striatula Schloth. 

 and of StrophoHcUa hyhrida H. & "W. 



The ramifying burrows extend parallel to the surface as well as 

 obliquely and vertically to it and are generally filled with some 

 foreign substance which, if softer than its surrounding walls, 

 crumbles out leaving them open ; as the outside of the brachiopod 

 shell weathers away the underlying borings appear on the new 

 surface as delicate intersecting grooves. This labyrinthine maze 

 of passages often weakens the shell causing it to disintegrate. 

 A single valve containing many borings was cut and polished 

 but none of the tubes were found to perforate the inner surface, 

 showing that in case the sponge inhabited the shell of a living 

 brachiopod it did not disturb the occupant in the least. 



This genus of sponges lives in our modern seas and ' ' ' burrows 

 in the shells of oysters and other bivalves, but for protection not 

 food.'' (Parker and Haswell. Textbook of Zoology. Vol. 1. p. 

 116.) 



It is not known how the process of boring is effected, ''the 

 presence of an acid in the tissue was suspected, but has been 

 searched for in vain". (Hartog. Sollas. Hickson. Macbride. 

 Protozoa, Coelenterates. and Echijwderms. p. 218.) Zittel says 

 that they "secrete pin-shaped siliceous elements .... by means 

 of which they bore labyrinthic passages in the shells of mol- 

 luscs". (Zittel. Textbook of Paleontology. Vol 1. p. 46.^ ''The 

 characteristic borings of Cliona are known from the Tertiary. 



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