LOWER HELDERBEEG ROCKS. 187 



Tentaculites irregularis ( n.s.). 



Plate VI. Fia. 22 & 23. 



Tentaeidites omaiut : Vanuxem, Final Rep. on the Geology of the Third District, 1842, p. 112, f. 3. 



— — Mather, Final Rep. on the Geology of the First District, p. 349, f. 3. 



Not T. omtrfu*, SoTTEBBT in Sil. System, pa. 628, pi. 18, f. 25; and Siluria, pi. 16, f. 11. 



Body small, acicular, tapering to an acute point. Annulations rounded, 

 unequally distant, from six to twelve in the space of one-eighth of an 

 inch : intermediate spaces marked with rounded annulating striae. 

 Length rarely more than half an inch. 



The tube is long and slender, and the annulations frequently do not extend to 

 the apex, often leaving that portion smooth for an eighth of an inch or more. This 

 character, however, as well as the unequal distribution and unequal strength of 

 the larger annulations, is subject to much variation; and this irregularity is one of 

 the most distinctive characters. 



The species is extremely abundant on the thin layers of the Tentaculite limestone, 

 surfaces of many inches square being often filled as completely as the fragment 

 represented in fig. 22. The layers thus covered are known in numerous places over 

 an extent of country from thirty to fifty miles, showing the myriads of these crea- 

 tures that flourished upon the bottom of the ancient sea. 



Fig. 22. A small portion of the surface of the stone, showing the abundant distribution of 

 these bodies. 



On this same specimen, which has a length of five inches and an average 

 breadth of a little more than one inch, more than five hundred individuals maj 

 be counted ; and the layer beneath, for the- thickness of a quarter of an inch, is 

 composed almost entirely of these fossils, giving more than ten times as many 

 as can be seen upon the surface. 



Fig. 23. Enlargement of a single individual. 



Geological position and locality. In the Tentaculite limestone at the base of the 

 Lower Helderberg group : Helderberg mountains, in numerous localities in Albany 

 county; Schoharie, Carlisle, Cherryvalley; near Fort-Plain, Catskill, near Sauger- 

 ties, Hudson, etc. 



f Pal^eontoloot IIL] 18 



