DIGTYONINE HEXACTINELLID SPONGES 187 



DICTYONINE HEXACTINELLID SPONGES FROM THE 

 UPPER DEVONIC OF NEW YORK 



BY JOHN M. CLARKE 



(Plates 10-11) 



A most striking characteristic of the shallow water fauna of 

 the Chemung beds of the middle Upper Devonic is its great de- 

 velopment of Hexactinellida, or silicious reticulate 

 sponges. The evidence of the fruitfulness and multiplicity of 

 these organisms at that time is of comparatively recent date. By 

 the publication of Memoir no. 2, of the State museum (The pale- 

 ozoic hexactinellid sponges constituting the family Dictyospongidae, 

 1899) more than 70 species of the fossils, assigned to 16 

 genera, have been made known from this formation. The 

 demonstration of such an extensive development could have been 

 possible only with the assistance of very large collections, and 

 while these have shown that such fossils abound in a most unfore- 

 seen profusion, yet it is clear that the}^ are more or less localized 

 in their distribution. At present they appear to have multiplied 

 most rapidly and varied most in the Chemung rocks of the cen- 

 tral and southwestern parts of the state of New York, particularly 

 in southern Ontario, Steuben, Allegany and Cattaraugus counties. 

 In these regions various well defined plantations have been 

 located, some of which have already yielded, and others doubtless 

 would yield on exploitation, thousands of individuals. Eastward 

 in the outcrops of this formation, these sponges become of rare 

 occurrence, and outside of this state but very few have been found 

 in rocks of this age. All of the forms hitherto described have 

 been embraced within the somewhat conventional limits of the 

 family Dictyospongidae, and have been shown to belong 

 to the hexactinellid suborder, Lyssacina. 



In the species of this suborder the skeleton is distinguished by 

 the independence of the spicular elements. Whatever the modi- 

 fication which the fundamental hexactin may have undergone, 

 however unlike in its various expressions, yet each spicule is inde- 



