64 [Assembly 



lying close to the outside or back of the shell. Another form 

 has partitions curved in a simple convex form, and a siphuncle 

 placed in the interior, separate from the shell. In this species the 

 successive volutions simply touch each other, while in the former 

 each outer volution covers half the width of the inner one ; and 

 there is a third species, only about as broad as a half dollar, in 

 which the inner coils are entirely covered by the outer ones. 



The Orthocerata are very perfect, the more common form being 

 a long tapering species, about two feet in its greatest length ; 

 others being pear-shaped ; and there are one or two shells which 

 seem between Ortkoceras and Goniatites, being bent into a sort of 

 crescent. These have knobs or bosses on every second or third 

 chamber. 



These fossils are found most abundantly in the lower part of 

 the upper layer, in which they sometimes lie very thickly. A 

 mass of this layer is placed in a separate case in one of the north 

 windows, which contains four perfect goniatites of the species 

 first mentioned, two or three broken ones, and several other 

 fossils. A recent JYautilus umbilicatus, from the tropical seas, 

 lies beside them, and the close resemblance in their general form 

 is very striking. 



The top of the upper layer often contains small coiled shells, 

 probably of the Genus Pleurotomaria ; and a tiny trilobite of 

 the Genus Proetus or ^onia is sometimes found in the base of 

 the lower layer. This rock also contains bones, plates and 

 spines of fishes, which are of great interest. A few specimens 

 are in the cases, appearing to belong chiefly to species of Astero- 

 LEPis (or " Star-scale "), a thick-plated fish, nearly allied to that 

 described in Hugh Miller's "Footprints of the Creator."* An 

 examination of these specimens will enable the student to recog- 

 nize such remains wherever he may find them ; and such will be 

 gladly received by the Curator of the Collection. 



The Marcellus slate is a rock of very wide extent, being trace- 

 able through Pennsylvania, Virginia, and even Tennessee ; and 

 it is a remarkable fact, stated by Prof. Rogers in his State 

 Report on the Geology of Pennsylvania, that through all this 

 distance it seems to contain near its bottom a thin argillaceous 

 limestone ; and that goniatites, of some variety, are found in this 

 slate in Pennsylvania and the West. This limestone and its re- 

 markable fossils have been clearly traced and examined in New- 



