2 1 6 NEW YORK STATE MUSEUM 



strata of the water which have dropped into the sediments below, then the 

 soft gray mud beds which throughout the region carry the fauna in its 

 highest development, must indicate the life of the water just above these 

 depths. That the shales are encroached on by sand deposits, thin at first 

 and eventually predominant, indicates only the distance from the shore line 

 to which the coarser terrigene detritus was carried. 



LAMELLIBRANCHIATA 

 The lamellibranchs of this fauna form a singular assemblage. Notwith- 

 standing the abundance and high development of certain expressions of the 

 cephalopods, particularly the Goniatite types Manticoceras, Gephyroceras, 

 Probeloceras, Sandbergeroceras, Tornoceras and others, it is yet quite fair 

 to say that the lamellibranch element of this fauna in both the eastern and 

 western subprovinces is its most distinctive characteristic. Into this faunal 

 province of Portage time strayed only an occasional representative of taxo- 

 dont or aviculoid shell, while the same sea in the contemporaneous east- 

 ward or Ithaca province fairly swarmed with them. On the other hand, at 

 no period in history have the peculiar genera Lunulicardium, Buchiola, 

 Praecardium, Paracardium, Honeoyea, Paraptyx, Ontaria, Pterochaenia, 

 Loxopteria, Tiaraconcha, Euthydesma, attained such development, indeed 

 for the most part never having appeared before or since. From the list of 

 70 species here described one may eliminate six or eight, and of the 

 remainder we shall find that all of these peculiar genera are knit together 

 by one striking characteristic, viz absence of denticulated hinge. There is 

 in all a most pronounced convergence to this structureless condition. 

 We find that species of this character are prevalent wherever the Intumes- 

 cens fauna is well developed, but at no other period of Devonic history 

 have they thus manifested themselves. Indeed, so far as the entire 

 Paleozoic succession of faunas is concerned, but once elsewhere does there 

 appear to have been such an outburst of these simplified lamellibranchiate 

 expressions ; this instance is the astounding manifestation of such shells in 

 the later Siluric stages (specially E) of Bohemia, whence Barrande has 

 portrayed an extended variety of species, whose detailed structure has yet 



