BLACK-KIVER LIMESTONE. 55 



Fig. 1. Natural long^itudinal section of a Gonioceras, showing a portion of the siphuncle, which is 



greatly expanded laterally between the septa, and contracted at their junction with it. In this 



specimen, the sides arc worn down below the angles of the shell, so that the septa do not 

 . . appear to turn backwards or towards the apex, as shown in 1 a, where the section is more 



directly through the angles. 

 Fig. 1 a. A longitudinal section, showing a small portion of the siphuncle at one extremity, and a more 



perfect exhibition of the curving septa towards the exterior of the fossil. 

 Fig. 1 b. A transverse section, showing the position of the siphuncle. The specimen on the upper side 



of the figure has been slightly worn, so as to present a straight line. The siphuncle is nearer 



to the upper edge than is represented in the figure. 

 Fig. 1 c. A transverse section near the smaller extremity of the shell, showing the position of the 



siphuncle. 

 Fig. 1 d. A small portion of the exterior denuded of the shell, showing only the central portion of the 



septa. 



Position and locality. In the Black-river limestone, and limited entirely to that mass. 

 Watertown, Jefferson county. 



{State Collection; Cabinets of the Albany Institute, of J. B. Crawe, and J. IIaix.) 



89. 1. ORxMOCERAS TENUIFILUM. 



■. ■ ■ Pl. XV. Figs. 1 a, b, c ; Pl. XVI. Figs. 1 a, b, c, d, e; and Pl. XVII. Figs. 1 a,b. 



Compare Orthoccratites crassiventris. Wahlenberg, 1S21, Petrefacta Telluris SuecanEe, in Nov. Act. Reg. 



Soc. Sci. Upsal, Vol. viii. p. 90. 



— — HisiNGEH, 1819, Anteckn V. Tab. iv. fig. 9. 



— — Id. 1837, Petref. Suec. Tab. x. fig. 3. 



Ormoceras Backii. Stokes, 1837, Geol. Trans. 2d series, vol. v. p. 709, referring to fig. 1, pi. 30 of vol. 1 

 .- 1 of the same work and same series. 



Conotubidaria Cuvierii. Troost, 1S3S, Memoires de la Societo Geologique de France, Tome iii. pag. SS, 



pl. 9, fig. 1 ; also fig. 7, pl. 10 of the same memoir. 

 Actinocei xs. Bronn, as figured by Stokes, Geol. Trans, ut supra. 



Elongated, subcylindric, somewhat gradually tapering to a very elongated conical form ; 

 siphuncle ventral, annulatcd or expanded into bladde.r-like rings at the junclion of the 

 septa ; septa moderately concave ; surface marked by longitudinal undulated fine thread- 

 like lines. 



The greatest expansion of the swelled portion of the siphuncle is just within the concavity 

 of the septum, and the constricted portion is just above the convexity of the septum. The 

 outer shell is thin, but it is connected with an interior one which often closely joins it by 

 infiltration of mineral matter, when it presents a thickened appearance. The septa are 

 likewise composed of double plates or lamina;, which separate and expand at the siphuncle, 

 folding round and forming the outer shell of this annulated tube. In cases where these 

 laminae separate a little nearer to the outer shell than in others, the rings, instead of being 

 obtuse or rounded at their edges, are angular. 



This species of Ormoceras occurs in immense numbers in the Black-river limestone. 



