40 DICTTOSPONGID.E. 



Boiryoilictya ramom in a soft sandy shale, near Mansfield, Tioga county, 

 Pennsylvania, the only locality at which it has been observed. 



Many of the sandstones of the Chemung series are rich in molluscan and 

 other fossils, constituting a profuse and diverse assemblage of organic life, but 

 the diffusion of this fauna is not uniform throughout the series. The fossils 

 predominate in rather thin layers separated by intervals of barren sands. Tlie 

 sponges, ho\ve\er, do not usually occur in these highly fossiliferous bands. 

 In the colonies at Bath and near Cohocton, the species of HYDNOCERAg have 

 almost no other organic associates and their prolific growth seems to have 

 crowded out other forms of life. Occasionally the cup of a Taxocrinus has 

 been found among the sponges at the latter locality but no other organisms 

 have been observed in the colonies at Bath. On the other hand, very near the base 

 of the Chemung group, on Hamlin's farm in the township of Naples, and not 

 over 150 feet above the last Portage fauna, is a colony of Hydnocekas where 

 the specimens, not well preserved on account of the laminated condition of 

 the sediments, are associated with these species : Avihoccelia iimbonata, var. 

 gregaria, Oyrtina Hamilton ensis, Stropheoclonta Cayuta, 8. vai'iahiUs, S. 

 arcuata, Leptostrophia perplana var. nervosa, Aviculopecten cancellatus, 

 SpJienotus sp., Arthracantlia sp. Three miles away, at Deyo basin, in the same 

 town, Hydnocekas occurs sparingly, with Ceratodictya, IIyduiodictya, 

 SpiHfer mesastrialis, Ati'ypa hystrix and Productella speciosa. 



In the upper part of the formation throughout the region in Allegany 

 county which has proved so prolific in Dictyosponges, these sjiecies ai-e fre- 

 quently associated with Spirifer disjunctus, Prodtwtella, Oamarotoxhia and 

 other brachiopods. 



Such a habitat for these sponges as is indicated by the foregoing evidence 

 is dissimilar to that of the recent hexactinellids. F. E. Sciiulze reports the 

 number of species dredged by the Challenger Expedition, from the bottom 

 of mud, clay or globigerina-ooze, as nearly twice that found on all other kinds 

 of bottom. Of about one hundred species, five were trawled from sand and 

 but two from gravel and stones. The Euplectellid^ and other forms pro- 

 vided with a root tuft were mostly found on soft muddy ground. Euplectella 

 aspergillnm was taken in mud at a depth of 95 fathoms, while K crassistellata 

 was dredged in radiolarian-ooze at the immense depth of 2750 fathoms, the 

 two species representing the extreme of depth at which the Hexactinellida 

 were found. 



These ancient allies and precursors of Euplectella seem to have been 

 adapted to different conditions of growth. They flourished and attained their 



