LOWER HELDERBERG ROCKS. 
ES7 
TentaciiMtes irregularis (n.s.). 
Plate VI. Fig. 22 & 23. 
Tentaculites ornatus : Vanuxem, Final Rep. on the Geology of the Third District, 1842, p. 112, f. 3. 
— —• Mahier, Final Rep. on the Geology of the First District, p. 349, f. 3. 
Not T. ornatus, Sowerby in Sil. System, pa. 628, pi. 12, 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 tire 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, shoving 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 may 
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. 
[ Palaeontology III.] 
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