BIRDSEYE LIMESTONE. 45 



ORTHOCERATA OF THE BIRDSEYE LIMESTONE. 



■ Plate XI. . 



78. 8. ORTHOCERAS MULTICAMERATUM. 



Pl. XI. Figs. 1 a, b, c. 

 • ■ Orthoceras multicameratum, Conrad in MS. Emmons, Geol. Report, 1842, p. 382. 



Extremely elongated, slender, very gradually tapering to an acute point ; surface 

 apparently smooth, or girt with slight undulations ; septa thin, gently arched, distant from 

 \ to yV the diameter ; siphvmcle a cylindrical ventral tube ; outer chamber very deep. 



The difference in the apparent concavity of the septa is owing to the wearing of the fossil 

 to different depths from the surface. The septa are very variable in their distance from 

 each other, being from i to ^'^ the diameter, and presenting even greater variations than 

 tliis, so that a single measurement would be no guide to the specific character. There will 

 be found in this species, and probal>ly in others, a proportion between the distance of the 

 septa and the diameter of the shell : where the diameter is greatest, the septa are pro- 

 portionally nearer ; and where smallest, comparatively more distant. This proportion, 

 however, is not always uniform ; for when similar diameters in different specimens are 

 measured, one presents a greater number of septa than the other. 



This species resembles the 0. tenuiseptum of the Chazy limestone, but I have not sufficient 

 evidence of their identity to unite the two. It occurs in great perfection in the Birdseye 

 limestone, and is almost the only well marked species found in this rock. Fragments of 

 several other species have been found, but none sufficiently characterized to merit description. 



Fig. 1. A fragment twelve inches long, showing a large part of the deep outer chamber, which is par- 

 tially filled with fragments of the Phvtopsis (See Plate IX). 



Fig. 1 a. Another fragment, showing the continuation of the fossil to the apex. These two were not 

 found in connexion, but are apparently fragments of two individuals. 



Fig. \ b. A fragment, showing some irregularity in the septa. 



Ficr. 1 c. A worn specimen, showing the septa and siphuncle which is near the margin ( ventral ? ). 

 The siphon, in one part, shows something like an enlargement between the septa as in 

 Ormoceras ; but it is too indistinct to warrant the reference. 



Position and locality. This fossil occurs principally in the higher and moreshaly portions 



of the Birdseye limestone, often surrounded and enveloped in fragments of the Phytopsis. 



Watertown, Jefferson county ; Mohawk valley. 



{State Collection ; Collection of the Albany Institute, i(e.) 



