UTICA SLATE AND HUDSON-RIVER GROUP. 313 



375. 2. ORMOCERAS CREBRISEPTUM. 



Pl. LXXXVI. Fig. 2 a; Pl. LXXXVII. Figs. 2 a, b, c, d, e. 



Elongated, conical, somewhat rapidly tapering to an acute apex ; septa numerous, 

 approximate, deeply arched, distant about one seventh the diameter ; siphuncle excentric, 

 enlarging in each cell and contracting at its passage through the septum ; section circular ; 

 surface marked by longitudinal lines, which are visible in the cast. 



This species is readily recognized by its very approximate septa, which are highly 

 arched, differing in this respect from the Orthoceras multicameratum of the Birdseye lime- 

 stone ; the siphuncle is also proportionally larger, and more excentric. 



Plate LXXXVII. 



Fig. 2 a. A part of the outer chamber of this species. 



Fig. 2 6. A fragment still preserving a portion of the shell, which shows some strong longitudinal 



striae, and the dorsal line or ridge, a character rarely observed in the Orthocerata. 

 Fig. 2 c. A fragment, showing the position of the siphuncle on the highly arched septum at the upper 



extremity of the figure. 

 Fig. 2 i. A fragment of stone, with numerous small speciniens of this species, associated with crinoidal 



joints. 

 Fig. 2 «. A longitudinal section of a fragment, showing the deeply arched septa, and the alternate 



enlargement and contraction of the siphuncle. 

 Plate Ixxxvi, fig. 2 a. A fragment of the same species, the siphuncle being distinctly moniliform. 



Position and locality. In the shaly calcareous strata of the Hudson-river group at Turin, 

 Pulaski, Washingtonville, and other places. (.State collection.) 



376. 1. THECA? TRIANGULARIS. 



Pl. LXXXVII. Figs. 1 a, b, c, d. 



Bodies of a slender pyramidal form, flat behind and rounded at the larger extremity, 

 angular in front ; small extremity pointed ; section ( aperture ? ) triangular. The surface 

 shows no defined markings, though the outer covering is not preserved in the specimens 

 which I have seen. 



These bodies are of frequent occurrence in the shales of the Hudson-river group, but 

 I have been unable to satisfy myself of their relation to other organic forms, or their 

 independent nature. Capt. Portlock {Geol. Rep. Londonderry, pag. 470, pl. 29 a, figs. 6, 

 7 a, 7 6) has given some figures of similar bodies, which he refers, with some hesitation,  

 to the internal bone of a cephalopod. Our species presents the general characters of others 

 of this genus, which Prof. G. Forbes has shown to belong to the pteropodous mojlusca, 

 [ PaljEontology.] 40 



