34 PALiONTOLOOY OF NEW-YORK. 



ORTHOCERATA OF THE CHAZY LIMESTONE. 



Plate VIL * 



Fragments of several species of Orthocerata have been observed in the Chazy limestone, 

 though but few of them are sufficiently perfect to be identified from description. In general 

 aspect, some of these appear to be identical with those of the Black-river limestone ; but 

 there are others apparently peculiar to the Chazy limestone. 



59. 3. ORTHOCERAS RECTIANNULATUM (n. sp.). 



Pu VII. Figs. 2, 2 o. 



Cylindrical ; surface annulated by obtusely angular ridges, with broad curving depressions 

 between ; annulations distant a little more than one -third the diameter of the fossil ; 

 siphuncle small, distinct, excentric ; septa moderately convex. 



The septa are only visible on the extremity of the specimen, and being almost denuded 

 of the shell, the character of the surface is unknown. 



Fig. 2. A portioa of the fossil, nearly two inches long, exhibiting eight annulations. 

 Fig. 2 a. Transverse section, showing the position of the siphon. 



Position and locality. In the grey crystalline central portions of the limestone at Chazy, 

 Clinton county. estate ColUetion.) 



60. 4. ORTHOCERAS SUBARCUATUM (n.fp.). 



Pu VII. Fig. 3. 



Cylindrical, gradually tapering, slightly arcuated, marked by angular ridges which are 

 equidistant and alternating with the sepia ; surface of shell smooth 1 ; septa distant from 

 \ Xo \ the diameter ; siphuncle not visible. 



This fossil resembles the last, but tapers more rapidly, and the annulations are more 

 acute. Another difference also is the slightly arcuate figure of the latter, which, if it be 

 found constant, may characterize the species. 



Position and locality. In the central dark-colored limestone, associated with Maelurea 

 magna, at Chazy, Clinton county. (*'«'< Collection.) 



