TKENTON LIMESTONE. 107 



The following figures present some variety of form, which this species assumes, under 

 different circumstances and in distant localities : 



Fig. 3 a. A specimen showing but a slight difference from the last described species. It is marked by- 

 distinct concentric wrinkles upon the disc ; is finely striated, with more prominent elevated 

 ones alternating with every four, five or six of the smaller ones. In this respect it partakes 

 of the characters of the specimen fig. 1 », which appears to me clearly referable to fu. 

 alttrnata. 



Fig. 3 b. This specimen presents the same form as the last, except that it is more produced in front. The 

 concentric wrinkles on the front are perhaps more distinct, and the shell is contracted more 

 abruptly just below the extremity of the cardinal line, producing small acute ears. 



Fig. 3 e. Lateral view, showing the elevation of the shell. 



Figt 3 i. A specimen of this shell, of nearly the same form as the last. The concentric wrinkles are 

 more distinct, and the radiating strise are equal, except on the central part of the shell, where 

 they are stronger. The shell is not entirely developed to the margin, and therefore does not 

 appear so much elevated as the last. 



Fig. 3 «. A larger specimen, with the disc distinctly wrinkled and marked by nearly equal radiating 

 strisB ; scarcely produced in front. The stria on the centre are more distinct than at the 

 sides. 



Fig. 3/. A very perfect specimen in form and markings. This drawing is by Mr. Conrad, from a 

 specimen now in my possession. The striae are a little stronger on the middle of the shell, 

 and in some parts alternate with smaller ones. 



It is certainly often very difficult to draw the line of distinction between this species and 

 the L. altemata, and more particularly so between this and L. camerata. Again, on the 

 other hand, it approaches very close, in some of its forms, to the succeeding species ( L. 

 tenuistriata ) ; but these two, when well preserved, are clearly and decidedly distinct. 



The figures of this species, given by Mr, Vanuxem and Dr. Emmons, scarcely show any 

 concentric wrinkles, and approach more nearly to the nasute form of L. alternate ( fig. 1 h, 

 pi. 31 A). 



Position and locality. This species is often abundant in the Trenton limestone, though 

 in many localities it is quite rare, or never seen. It abounds at Trenton Falls, and at Sugar 

 River in Lewis county. It is more rarely seen in the neighborhood of Little Falls, while 

 towards the north it is rarely found, and is scarcely known to me as occurring in the 

 Champlain valley. {State Collection.) 



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