24 PALEONTOLOGY OF NEW YORK. 



Lowei- 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. divaricatus, Hall. The last 

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

 Hamilton faunas, l)ut from the upper Devonian onward the species multiply 

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

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

 to the time value of the Apertukati was suggested by De V^erneuil, 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 

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

 dichotomous or intercalary. 



Spirifer arenosus, Conrad, Oriskany sandstone. 



Spirifer unicus. Hall, Corniferous limestone. 



Spirifer Whitneiji, Hall, Lower upper Devonian. 



Spirifer disjundus, Sowerby,! 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. 



*Geolog-ie de la Russie de I'Europe, p. 126, 1845. 



t A prefereiK-e is frequently expressed by the Continental writers for the term S. Verneuili, applied to 

 this species by Murchison in 1840. In regard to the priority of these name.s both introduced in the same 

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

 have used the name given by myself in honor of my friend De Vbrneuil to the Spirifer which abounds in 

 the same stratum [Verneuili-shales] in the Boulonnais. It is, however, the Spirifer disjunctus, having beeu 

 previously named by Sowehby." 



