46 PALAEONTOLOGY OF NEW YORK. 



In its superficial ornameutation, species of Cyrtina, like those of Cyrtia, 

 conform to a marked degree with that of the associated Spirifers. In the genus 

 Spirifsr it has been shown that the various modes of surface ornament have 

 a more or less definite time-value, and the same fact is, to a certain degree, true 

 of Ctbtina. In the fauna of the Niagara group the species C. pyramidalis. Hall, 

 has an exterior probably fimbriate like that of Spirifer sulcatus. The greatest 

 individual and specific development of these forms is in the Devonian where 

 the representatives are mostly coarsely plicate shells with smooth fold and 

 sinus, like the prevailing type of Spirifer of the same fauna. Among these are 

 C. Dalmani, Hall, of the Lower Helderberg, C. crassa, Hall, of the Corniferous 

 limestone, C. Hamiltonensis, Hall, of the Corniferous, Hamilton and Chemung 

 groups, C. triquetra, Hall, and C. umbonata, Hall, of the middle Devonian, and 

 C. acutirostris, Shumard, of the Choteau limestone. In the Oriskany sandstone 

 occurs C. rostraia, Hall, a large species with the exterior coarsely lamellose and 

 finely striated radially as in the associated Spirifer raricosta. C. biplicata, Hall, 

 of the Schoharie grit and Corniferous limestone is a somewhat variable form 

 with smooth exterior, low fold and sinus and obsolete lateral plications. Species 

 with plicated fold and sinus are, like the Spirifers, rare in the Devonian, but 

 become more frequent in the Carboniferous where the Aperturati predominate. 

 In the American Devonian, C. curvilineata. White, is the only form of this 

 character, and while this type is wanting in our Carboniferous faunas so far 

 as known, it is represented in the European Carboniferous by C. carbmaria, 

 McCoy, C. dorsata, McCoy, and C. septosa, Phillips, the last a large, broad- 

 winged species with the external expression of Syringothyris. In the Waverly 

 group of Ohio occurs the C. lachrymosa, sp. nov., a form with faint plications 

 and strongly pustulose surface covered, near the beak, by fine concentric lines. 

 The cherty beds of the Burlington series in Iowa contain an undescribed 

 species which in external aspect is extremely like the Spiriferinas of the 

 Keokuk and Chester groups, (e. g., S. subelliptica and S. transversa, McChes- 

 ney), having the surface covered with closely crowded, concentric and fimbriated 

 lamellae. 



