C. Callaway — L. Helderherg Group of'N. York. 275 



0. TuUievsis, Yanuxem. Of the type of 0. resupinata, Martin, of our Devonian 

 and Carboniferous. 



Streptorhynchus Ohemimgensis, Conrad. Similar to S. crenistria, Phil., of the Euro- 

 pean Devonian and Carboniferous. 



Strophodonta inequistriata, Conr. At one time identified hy Hall ■with Orthis 

 inter strialis, Phil,, and now doubtfully separated. 0. (?) interstrialis is a 

 Devonian fossil. 



S. nacrea, Hall, almost identical with S. lepis, Bronn. Devonian. 



Productella, gen. Species numerous. This genus is essentially a Prodticta, differ- 

 ing from it only in the possession of inconspicuous hinge-teeth and sockets. 

 Producta is characteristically a Carboniferous genus. 



Cyrtina Samiltonensis, Hall. Closely allied to C. heterocUta, Defr., of the De- 

 vonian limestone of Europe. 



Athyris spir if er aides, Eaton. Barely separable from A. eoncentrica, von Buch, an 

 Upper Devonian fossil. 



Atrypa aspera, Schlot. A common European Devonian form. 



Phynchonella venustula, Hall. Identified by Conrad with R. cuboides, Sow., one 

 of our common Devonian species ; but separated by Hall for some very slight 

 differences. 

 Cephalopoda. — Several species of G-oniatites have been foimd in the Marcellus 



Shale, the base of the Hamilton group. 

 Crustacea. — Phacops rana, Green. Closely representative of P. latifrons, Bronn, of 

 the British and Continental Devonian rocks. 



I rely less, however, upon indh'idual species than npon the 

 general facies of the fauna, and the relative proportions of the 

 numbers of the genera and species. In collecting in Western 

 New York, and in reviewing and arranging large series of speci- 

 mens in the New York State Museum, the forms which were 

 everywhere turning up were Spirifera, CJionetes, Strophodonta, Atrypa, 

 Cyrtina, and these of Devonian or even Carboniferous facies. The 

 genus Productella is also very significant. Of species the most 

 abundant are Orthis Vanuxemi, Strophodonta incsquistriata, Spirifera 

 miicronata, Athyris spiriferoides, Atrypa aspera, Cyrtina Hamiltonensis, 

 Heliophyllum Halli, and Phacops rana, all of them represented by 

 identical or closely allied forms in European Devonian or Carboni- 

 ferous rocks. On the other hand, the Ludlow-like Lamellibranchs 

 are comparatively rare. 



The formations underlying the Hamilton must also be taken into 

 account. In the Schoharie Grit, fishes make their first appearance ; 

 and, in the later epoch of the Upper Helderberg Limestone, this 

 class is abundantly represented. The types are clearly those of the 

 European Old Eed Sandstone. Macropetalichthys resemhles Pterichthys. 

 Forms like Cephalaspis and Holoptychius also occur. Of plants, 

 Caulopteris is found in marine limestones below the Hamilton group 

 in Ohio, and Lepidodendron is quoted by Professor Newberry from 

 the same limestone. Generally speaking, the fauna of the Upper 

 Helderberg is intermediate in character between the underlying 

 Lower Helderberg and the overlying Hamilton. 



The general testimony of the fossils is clearly in favour of the 

 Devonian age of the Hamilton group, and the exceptional character 

 of the lamellibranchiate fauna is probably to be explained on the 

 supposition that certain causes, biological or otherwise, retarded the 

 migration of the European Ludlow Conchifera to the western seas. 

 Their occurrence in the Hamilton would hardly seem to be sufficient 



