164 
PALAEONTOLOGY OF NEW YORK. 
are distinctly and strongly striated longitudinally, and the annulations are 
abrupt and well defined, varying considerably in their distance in different 
specimens. The collection before me consists of six separate individuals lying 
upon the surface of the stone, differing in the degree of curvature and in the 
strength of the annulations. There are five other sjiecimens, which are in 
groups of two, three or four individuals adhering together at their bases, or 
attached to some other body. Another single individual among these, shows 
the annulations nearly obsolete, and a thickening and irregular growth of 
the test. 
These characters are such as belong to the genus Cornulites, and have not 
been found in any true Tentaculites, so far as my observation has extended. 
If these Lower Silurian forms are to be recognized as Tentaculites, the 
definition of the genus must be extended in order to include them, and it 
would then embrace very incongruous material. 
In the comparison of individual specimens, it may not always be practicable 
to distinguish Tentaculites from Cornulites; but under an ordinary magnifier 
the surface of the latter presents, in most examples, a somewhat different texture, 
and the annulations are usually less abruptly elevated, and often sloping equally 
in both directions. In nearly all the American species of Tentaculites the 
striae are transverse, and in perfect specimens usually marking, in a greater 
or less degree, not only the interspaces but the annulations. This feature, 
however, may be obscure from age or wearing, or may in some species not 
exist at all. On the contrary, the species of Cornulites are always longitu¬ 
dinally striated, and in their young state the annulations show little variation 
in their character and general aspect. The external basal portions of both 
Cornulites and Tentaculites are often free from annulations. In the latter, 
the annulations become stronger on receding from the base of the fossil, while 
in older individuals of the former they often become less marked, and finally 
obsolescent; they are likewise frequently irregular in their development, 
projecting more on one side than upon the other, and otherwise subject to 
variations which are not observed in Tentaculites. At the same time some 
