486 Systematic Paleontology 



It is not always easy to distiuguish this species from T. aculus; but in 

 the hitter the annulations are more closely and regularly arranged, espe- 

 cially on the earlier portions of the shell. In New York this species occurs 

 in both the Helderberg and the Oriskany. 



Occurrence. — Helderberg Formation, Coeymans Member. Dawson. 

 New Scotland Member. Devil's Backbone. Oriskany Formation, 

 Shriver Member. Cumberland, west side of Queen's Point opposite 

 Keyser, Winchester Eoad near Allegany Grove. 



Colleclions. — Maryland Geological Survey, U. S. National Museum. 



[Ohern.] 

 Tentaculites gykacanthus (Eaton) 

 Plate LX XXVII, Fig. 11 



Echinus gyracanihus Eaton, 1832, Geological Text Book. 



Tentaculites ornatus Vanuxem, 1842, Final Rept. on the Geol. of the 3d Dist. 



N. Y., p. 112, fig. 3. 

 Tentaculites ornatus Mather, 1843, Final Rept. on the Geol. of the 1st Dist. 



N. Y., p. 349, fig. 3. 

 Tentaculites irregularis Hall, 1859, Nat. Hist. N. Y., Pal., vol. iii, p. 137, pi. vi, 



figs. 22, 23, 18G1. 

 Tentaculites gyracanthus Hall, 1888, Nat. Hist. N. Y., Pal., vol. vii, p. 5 



(supplement to vol. v), pi. cxiv, figs. 7-13. 

 Tentaculites gyracanthus Weller, 1903, Pal. N. J., vol. iii, p. 264, pi. xxiv, 



figs. 19, 20. 



Description. — " Body small, acicular, tapering to an acute point. An- 

 nulations rounded, inequally distant, from six to twelve in the space of 

 one-eighth of an inch : intermediate spaces marked with rounded an- 

 nulating striae. Length rarely more than half an inch." Hall, 1859. 



" Shell elongate, circular in cross-section, annulate, gradually tapering 

 to the apex. Annulations smooth, rounded, situated at irregular in- 

 tervals, from one to three in the space of 1 mm. ; the interspaces between 

 the annulations are marked by fine, annular strife. In internal casts the 

 annulations are smaller and the fine, annular striae are lacking from the 

 interspaces." Weller, 1903. 



This species occurs in great numbers in the Manlius formation of the 

 Upper Silurian of New York and gave to this horizon its hrst name 

 (Tentaculite limestone). It also occurs in large numbers in the Tonolo- 



