164 PALEONTOLOGY OF NEW YORK. 



are distinctly and strongly striated longitudinally, and the ambulations are 

 abrupt and well defined, varying considerably in their distance in different 

 KjK'i-iiiiens. 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 specimens, 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 Cobnulites, 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 

 stria? 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 winch are not observed in Tentaculites. At the same time some 



