46 PALEONTOLOGY OF NEW-YORK. 
79. 9. ORTHOCERAS RECTICAMERATUM. 
Pu. XI. Fig. 1 d. 
Elongated, cylindrical, gradually tapering ; septa not curved, but passing obliquely in a 
line from the inside of the shell to the siphuncle, or vice versa ; siphuncle a cylindrical 
tube, somewhat excentric ; septa distant } to #, 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 OrTHOCERATA, 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 CepHatopopa belonging to other 
genera, and some species of the Gastrropopa which subsequently appear in the succeeding 
limestone. 
The OrtHocerata and other CepHatopopa 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. 
