56 PAUKONTOLOOy OF NEW-YOKK. 



The rock is very compact, and the fossil cannot be easily obtained except in weathered 

 portions of tlie mass. Most of those figured, and nearly all the specimens usually seen, 

 are found upon the weathered surfaces of the rock, where it presents such a variety of 

 appearances as to lead one to believe there are several species. In examples like those on 

 Plate XVI. they are commonly regarded by the inhabitants of the neighborhood as the 

 vertebrae of fishes, to which they bear some remote resemblance. 



I have little doubt of tlie identity of this fossil with those cited above ; though since there 

 is not absolute certainty, I have adopted another name until this can be determined. The 

 specimens of Mr. Stokes are from a locality where the existence of other well known fossils 

 induces us to refer the rock to the lower stages of our system, and probably to a position 

 precisely corresponding to the thin mass containing these fossils upon the Black river. The 

 specimens of Mr. Troost, though said by that gentleman to be associated with many from 

 the younger silurian strata and some carboniferous fossils, I am well aware are from a 

 position quite as low in the series as the Trenton limestone of Ne\v-York. It is true, Mr. 

 HisiNGER has referred his Orthoceratites crassiventris to the more recent transition strata of 

 Sweden, which would be a strong indication of its being a different species, if there be no 

 error in regard to position.* 



Platb XV. 



Fig. 1. A fragment of this species, partially covered with the delicate thin outer shell, presenting in the 

 lower part of the figure some obscure markings of the septa ; and above, showing the 

 moderate convexity of a septum. 



Fig. 1 a. Transverse section of the same specimen, broken through the annulations of the siphon. 



Fig. 1 b. A portion of the outer shell magnified, showing the fine undulating threadlike lines upon the 

 sur&ce. {Specimen from tht Cabinet of the Albany Institute.) , 



Fig. 1 c A longitudinal section of a portion of a large individual, showing the septa, which are com- 

 posed of double plates reaching only to the inner lamina of the exterior shell. The distance 

 between the laminee is unusually great in the upper part of this specimen, the spaces between 

 them being nearly as great as between the septa. 



Plate XVI. 



Fig. 1. A transverse section, showing the edge of an annulation of the siphon, and the proportionate size 

 a( this part of the fossil. (By a mistake of the artist, the upper edge of this ring is far too 

 nearly central to' be true.) 



Fig. 1 a. An artificial longitudinal section of a portion of fig. 1, pi. 15, showing the siphon and septa. 



Fig. 1 J. A longitudinal section, in a direction from ihe ventral to the dorsal side, showing very clearly 

 the position of the siphuncle. The specimen appears contracted at both extremities, which is 

 due to its having been slightly bent, so that in wearing do\vn, the two extremities are worn 

 beyond the centre, while the middle portion is central, showing the siphuncle almost in 



* The structure of siphuncle here represented, though common in the lower, is rare in the higher strata ; and 

 ilthough we have something approaching to the same form, yet I have not hitherto been able to detect precisely the 

 •HDe in any of the Orthocerata of more recent periods than the Hudson-river group. 



