24 PALEONTOLOGY OF NEW YORK. 



Lower Helderberg fauna we have but the single species, S. concinnus, Hall ; in 

 the Oriskany sandstone, S. arenosus, Conrad ; in the Corniferous limestone, 

 S. unicus. Hall {= S. arenosus), S. Grieri, Hall, and S. divaricattis, Hall. The last 

 named species is the only representative of this type of structure in the 

 Hamilton faunas, but from the upper Devonian onward the species multiply 

 rapidly, becoming most abundant and varied in the different faunas of the lower 

 Carboniferous and continuing until the close of palaeozoic time. The key-note 

 to the time value of the Aperturati was suggested by De Verneuil, who 

 divided them into two subsections, " the first including species with fine, not 

 dichotomous plications, all of which belong to the Devonian system ; the second 

 including those with broad [simple] plications or those which have the plica- 

 tions fine and always dichotomous. Spirifers of the last division are all 

 Carboniferous or Permian."* With some reservation this statement is emi- 

 nently true of the American Aperturati, with which alone in the following 

 classification we have to deal. 



(a) Disjunctus-type. Forms with well developed fold and sinus, elongate 

 binge and elevated cardinal area ; lateral plications simple, median plications 

 dichotomous or intercalary. 



Spirifer arenosus, Conrad, Oriskany sandstone. 



Spirifer unicus, Hall, Corniferous limestone. 



Spirifer Whitneyi, Hall, Lower upper Devonian. 



Spirifer disjundus, Sowerby,f Chemung group. 



In the higher Chemung sandstone of Alleghany and Cattaraugus counties, 

 N. Y., there is a well defined variety of this species which is of not uncommon 

 occurrence. It is distinguished by a conspicuous median sulcus on the fold 

 and has been well figured in Palaeontology of New York, Volume IV, pi. xli, 

 figs. 10-16. We propose to distinguish it by the varietal term sulcifer. 



*0^1ogie de 1* Euasie de I'Europe, p. 126, 1846. 



t A preference is frequently expressed by the Continental writers for the term iS. Vemeuili, applied to 

 this species by Mubchison in 1840. In regard to the priority of these names, both introduced in the same 

 year, MuiiOHnoa has said in the 3d edition of his " Siluria" (p. 422, 1859) : " Von Dbchbn and his associates 

 have used the name given by myself in honor of my friend Db Vbkneoil to the Spirifek which abounds in 

 the same stratum [Vemeuili-shales] in the Boulonnais. It is, however, the iSpirifer disjunctiis, having beeu 

 previously named by Sowbrjit.'' 



