THE GREAT GLASS-SPONGE COLONIES OF THE 



DEVONL^N; THEIR ORIGIN, RISE, AND 



DISAPPEARANCE 



JOHN M. CLARKE 



New York State Museum, Albany 



A very striking feature of the biota of the Devonian as repre- 

 sented in the state of New York is the extraordinary development 

 in its late stage, the Chemung period, of its silicious hexactinelHd 

 sponges. At various levels in the sandy deposits of this time they 

 are found, sometimes as scattered individuals and sometimes in 

 plantations of uncounted numbers, so that it is safe to say that from 

 the bottom of the formation in the "southern tier" of counties to 

 near its summit, the hexactinellids of this order, the Dictyospongida, 

 are many times more abundantly represented than in all the rest of 

 the world together. In their extensive monograph of these sponges 

 Hall and Clarke ascribe seventy-seven species in sixteen genera to 

 this formation within the borders of New York and the same rocks 

 in northern Pennsylvania. Clarke has described a number of 

 additional Chemung species, so that there are now about ninety 

 outstanding specific designations for this Devonian assemblage. 



Sometime it will be a subject for discussion among morphologists 

 whether this so-called order, Dictyospongida, is homogeneously 

 constituted ; probably it is not, but so seldom is the spicular struc- 

 ture retained in the sandy matrix that on the basis of general form 

 and habit, and the arrangement of the spicular bands which are 

 usually sharply preserved in impressions, all the sponge occurrences 

 in this formation and those of Uke composition in the Mississippian 

 faunas of Ohio and Indiana are now for convenience put in this 

 single group. That they are for the most part accurately referred 

 to the hexactinellids is abundantly shown by the spicular structure 

 of the Mississippian species which has been demonstrated. The 

 described species and genera have been established with the best 



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