46 PAUEONTOLOGY OF NEW-YORK. 



79. 9. ORTHOCERAS RECTICAMERATUM. 

 Pt. XI. Fig. 1 d. 



Elongated, cylindrical, gradually tapering ; septa not curved, but passing obliquely in a 

 line from ihe inside of the shell to the siphuncle, or vice versa ; siphuncle a cylindrical 

 tube, somewhat excentric ; septa distant ^ to j\ the diameter. 



This species bears considerable analogy to the last in some respects ; but it differs in the 

 direction of the septa, which are not curved ; in tapering more rapidly, and in the siphuncle 

 being less excentric. The specimens obtained give only partial opportunities of seeing the 

 exact position of the siphuncle, which differs essentially from the last. . 



Position and locality. It occurs in the same association as the last, and all the specimens 

 contain great numbers of fragments of Phytopsis. Watertown, Jefferson county ; Mohawk 

 valley. 



BLACK-RIVER LIMESTONE. 



Succeeding the Birdseye limestone, we have a well-defined mass of greyish blue lime- 

 stone, very compact and sometimes subcrystalline in texture. This has already been fully 

 described, and is known as the Black-river limestone. It probably rarely or never exceeds 

 ten feet in thickness ; but from being characterized by a large number of peculiar fossils, 

 though mainly belonging to a single family, it is regarded as worthy of a separate notice. 



The principal and most prominent organic bodies in this rock are Orthoceeata, some of 

 which attain the astonishing length of more than ten feet, and have a diameter of one foot 

 or more. Associated with these are several species of Cephalopoda belonging to other 

 genera, and some species of the Gasteropoda which subsequently appear in the succeeding 

 limestone. 



The Oethocerata and other Cephalopoda of this rock, so far as I have been able to 

 ascertain, differ from any in the Trenton limestone ; and it would therefore appear that 

 nearly every species perished at the close of this period. Several species, one of Pleuro- 

 tomaria, and a few others, are identical with those of the Trenton limestone, and it is by 

 these only that it is linked with the succeeding rock. Its organic affinities, however, are 

 very close ; for in both this limestone and the. Trenton, great numbers of Orthocerata 

 occur, though of different species. 



