SPONGES. 211 



AMERICAN PALEOZOIC SPOXGES. 



Although the spongia? attained the height of their develop- 

 ment in Mesozoic and subsequent eras, they were also very nu- 

 merously represented in palaeozoic times, in fact, much more so 

 than is generally known or suspected. As a rule they cannot 

 be considered common fossils, and, generally, belong to the 

 rarities. There are, however, several notable exceptions, such 

 as the Dictyophyton layers of the Chemung in New York, the 

 Astrlospongia beds in the Niagara of Tennessee, and the more 

 recently discovered sponge layer near the base of the Trenton 

 in northern Illinois, which has delivered up to the untiring 

 efforts of Dr. Oliver Everett, of Dixon, 111, the most varied and 

 interesting collection of sponges so far discovered in America. 

 The author, too, has during the last ten years, diligently 

 searched the lower rocks for remains of these long neglected 

 fossils. The material found was carefully preserved, and, since 

 the publication of Prof. ZitteFs sj^stem of classification, much 

 time has been spent in the attempt to work out the microscopic 

 structure. Owing to the poor state of preservation, the at- 

 tempt often proved quite unsuccessful, yet on the whole the re- 

 sults were satisfactory. They seem to establish, that the ma- 

 terial at hand from horizons below the Devonian represents no 

 less than thirty-four genera.* Of these, twenty-two have been 

 described: Protospongiti by Salter; Arch&ocyathus, Calathium, 

 Eospongia, Trachyum, Trichospongia and Avlocopina by 

 Billings: Aulocopium by Oswald; Brachiospongia by Marsh; 



* Including ArchceocyatJnis and Ethmophy Hum, two genera that may not be true 

 sponges, certain features of their structure, lately pointed out. seeming to indicate a 

 closer relationship with the corals. 



