Helderberg Formation in Mahyi.am) 47 



Order OPISTHOBRANCHIATA 



Suborder CONULARIDA 

 Family TENTACULIDAE 



Genus TENTACULITES Sdilotheim 



Tentaculites gyracanthus (Eaton) 

 Plate LXXXVII, Fig. 11 



Echinus gyracanthus Eaton, 1832, Geological Text Book. 



Tentaculites ornatus Vanuxem, 1842, Final Kept, 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, 1861. 

 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, aciciilar, tapering to an acute point. An- 

 niilations roiiuded, inequally distant, from six to twelve in the space of 

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

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



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

 to the apex. Annul ations 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 strife are lacking from the 

 interspaces." Weller, 1903. 



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

 Upper Silurian of Xew York and gave to this horizon its first name 

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

 way formation and locally in the upper part of the Keyser member of the 

 Helderberg, 



Length 5.6 mm.; diameter .7 mm. 



Occurrence. — Helderberg Formation, Keyser Meaiber. Keyser, 

 West Virginia; Dawson, Devil's Backbone, Tonoloway, Maryland. 



Collection. — Maryland Geological Survey. 



