lo NORTH AMERICAN INDEX FOSSILS. 



"23. S. rugosa Billings. (Fig. 1218,;.) Cambric. 



Shell small, straight; surface unknown. The weathered speci- 

 men figured shows the projecting edges of the several ensheathing 

 cones. 



Lower Cambric of Labrador. 



24. S. curvata Shaler and Foerste. (Fig. 1218,^.) Cambric. 



Shell curved, tapering rather rapidly; surface smooth or marked 

 by scarcely visible transverse striae. 

 ' Lower Cambric of Labrador, Quebec and Massachusetts. 



Family Tentaculitid^ Walcott. 



IX. Tentaculites Schlotheim. 



Shell straight or slightly curved, elongate, tapering, conical, 

 with circular cross section and terminating posteriorly either 

 acutely or in a bulb. Surface marked by strong transverse rings 

 which are closely arranged near the apex and more distant and 

 stronger near the mouth. Fine transverse and rarely longitudinal 

 striae are present. Apical portion often filled with calcareous 



P^IG 1220. Tenlaculiies gyracanihus, y/'ith. erAoxgQmeui. (After Hall. ) 



matter or divided off by transverse septa. Ordovicic-Devonic. 

 (Extremely abundant in the Siluric and Devonic.) 



25. T. gyracanthus (Eaton). (Fig. 1220.) Siluric. 



Annulations irregular in strength and distribution, being from 

 6 to 12 in the space of one eighth of an inch. Length rarely more 

 than one half inch. 



