ATRYPA OF THE UPPER HELDERBERG GROUP, &o. 
317 
Terebratulites explanatus : Schloth., Ibid. pi. xviii, f. 2. 
Atrypa reticularis: Dalman Vet. Ac. Handl., pi. iv, f. 2. 1827. 
“ 11 Hisinger, Lethe* Suecica, pi. xxi, f. 11. 
Terebratula prisca: Von Buch, Ueber Terebratulen, p. 71. 1834. 
Atrypa affinis : Sowerby in Murchison’s Silurian System, pi. vi, f. 5. 1839. 
Delthyris prisca: Fahrenb. in Bull. Mosc., p. 788. 1844. 
Terebratula (Atrypa) prisca: Phillips, Figures and Descriptions of the Palaeozoic Fossils of Cornwell. 
Devon and West Somerset, pa. 81, pi. xxxiii, f. 144. 1841. • 
Terebratula insperata : Phillips, Ibid, pa. 83, pi. xxxiii, f. 18. 1841. 
Spirifer affinis: Sowerby, Trans. Geol. Soc. Lond. 2d series, Vol v, pi. Ivii, f. 11. 
Terebratula prisca: d’Archiac et de Verneuil, Trans. Geol. Soc., Lond. 2d series, Vol. vi, p. 392. 
“ ‘‘ A. Koemer, Die Versteinerungen des Harzgebirges, pi. v, f. 11-13. 1842. 
“ reticularis : de Verneuil, Geol. of Russia and Ural Mts., Vol. ii, pi. x, f. 12. 1845. 
Atrypa lentiformis : Vanuxem; 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. 
c ' “ Bronn, Index Palseontologicus, p. 1248. 1848. 
Spirigerina reticularis: d’Orbigny, Prodrome, Vol. i, p. 99. 1849. 
Terebratula prisca : Quenstedt, Handbuch der Petrefactenkunde, p. 461, t. xxxvii, f. 1-4. 1851. 
Atrypa reticularis: Davidson, British Fossil Brachopoda, Introduction, Vol. i, pi. vii, f. 87-93. 1853. 
? Terebratula squamifera pars : Schnur, Dunker und Von Meyer’s Palaeontographica, Vol. iii, p. 181, f. 4, 
“ insquamosa: Ibid, Vol. iii, p. 182, f. 5. 1853. 
“ zonata [?] Ibid, Vol. iii. p. 182. 1853. 
Atrypa reticularis : Morris, Catalogue of British Fossils, p. 132. 1854. 
Anomia “ Sharpe, in Hanley’s “ Ipsa Linnaea Conchylia,” p. 127. 1855. 
Spirigerina “ M'Coy, British Palaeozoic Fossils, p. 379. 1852. 
“ “ Sandberger, Die Brach. des Rhein. Schichten. in Nassau, pa. 51, pi. xxxiii, f.l. 1851. 
Atrypa “ Woodward, Manuel of the Mollusca, 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, Palaeontology, Vol. iii, p. 253, pi. xlii, f. 1. 1862. 
“ “ Davidson, 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 
