r 



ATRYPA OF THE UPPER HELDERBERG -GROUP, &c. 317 



Terebratulites explanatus : Schloth., Ibid. pi. xviii, f. 2. 



^trypa reticularis : Dalman Vet. Ac. Handl., pi. iv, f. 2. 1827. 



" " HisiNOEE, Letheie Suecica, pi. xxi, f. 11. 



Terebratula prisca : Von BucH, Ueber Terebratulen, p. 71. 1834. 



Atrypa affinis : Sowerbt in Murchison's Silurian System, pi. vi, f. 5. 1839. 



Delthyris prisca: Fahrknb. in Bull. Mosc., p. 788. 1844. 



Terebratulif (Mrypa) prisca : Fhilups, Figures- and Descriptions of the Palaeozoic Fossils of Cornwell. 



Devon and West Somerset, pa. 81, pi. xxxiii, f. 144. 1841. 



Terebratula in^erata : Phillips, Ibid, pa. 83, pi. xxxiii, f. 18. 1841. 



Spiri/er affinis : Sowkbbt, Trans. Geol. Soc. Loud. 2d series, Vol v, pi. Ivii, f. 11. 



Terebratula prisca : d'Abchiac et db Vehnkuil, Trans. Geol. Soc., Lond. 2d series. Vol. vi, p. 392. 



" " A. RoEXER, Die Versteinerungen des Harzgebirges, pi. v, f. 11-13. 1842. 



" reticularis : de Vebnecil, Geol. of Russia and Ural Mts., Vol. ii, pi. x, f. 12. 1845. 

 Mrypa lentiformi* : Vakuxim; A. affinis, and tribulis, Hall, Geology of the State of New York. 1843. 

 Hipparionyx consimilaris : Vanuxem, Geol. Report of the Third District N. York, p. 132, f. 2. 1843. 

 Terebratula reticularis ; Barrande, Ueber die Brach. Silur. Schichten von Boehmen, pi. xix, f. 8. 1847. 



'• " BaoNN, Index Palaeontologicus, p. 1248. 1848. 



Spirigerina reticularis : d'Oebio.nt, Prodrome, Vol. i, p. 99. 1849. 



Terebratula prisca : Qoenstedt, Handbuch der Petrefactenkunde, p. 461, t. xxxvii, f. 1-4. 1851. 

 Atrypa reticularis: Davidsos, British Fossil Brachopoda, Introduction, Vol . i, pi. vii, f. 87-93. 1853. 

 t Terebratula squami/era pars : Schmor, Dcnkeb und VoM Meter's Palaeontographica, Vol. iii, p. 181, f. 4 



" ijMjuamojo; Ibid, Vol. iii, p. 182, f. 5. 1853. 



" zonata [?] Ibid, Vol. iii. p. 182. 1853. 



Mrypa reticularis : Morris, Catalogue of British Fossils, p. 132. 1854. 



jinomia " Suarpe, in Haniey's " Ipsa Linnsea Conchylia,'' p. 127. 1855. ' 



Spirigerina " M'Cot, British PaliEozoic Fossils, p. 379. 1852. 



" " Sandberoer, Die Brach. des Rhein. Schichten. in Nassau, pa. 61, pi. xxxiii, f.l. 1851. 



Mrypa " Woodward, Manuel of the MoUusca, p. 228, f. 144, 145; and plate xv, f. 21. 1856. 



•' " Hall, Report on the Geological Survey of Iowa, pi. vi, pp. 4, 5. 1858. 



" Hall, Nat. Hist, of New York, Paleontology, Vol. iii, p. 253, pi. xlii, f. 1. 1862. 



" " Davidsoh, Monograph of British Devonian Brachiopoda, part vi, p. 53. 1864. 



I have heretofore referred to Atrypa reticularis a species of this genus in 

 the Niagara and Lower Helderberg groups, which is allied to, or identical 

 with one of those occurring in the Upper Helderberg and Hamilton groups. 



There is, nevertheless, a character of individuality about the forms from 

 each of the geological periods, which serves to distinguish them from each 

 other ; and whether this difference shall be recognized as specific or varietal, 

 is perhaps of little consequence at the present time. Taking our collections 

 from the geographical area of New York, we can readily recognize the 

 specimens from each of the successive groups or formations ; and I am not 



