40 On the Bilobite. 



The name of Bilobite is not to be found in any modern 

 work on Oryctology ; and it is probable that its application 

 in this instance has been suggested by its peculiar appearance. 



With a view of calling the attention of naturalists to this sub- 

 ject, the following account is laid before the Society. 



They are imbedded in a loose friable sandstone which seems 

 to be almost wholly composed of organic remains, such as 

 productus, terebratula, &,c. The region is secondary, and 

 is described by Mr. Pierce, in vol. II. of Silliman's Journal, to 

 which we refer the reader. The explanatory figures, (see 

 Plate V.) would seem to indicate at least two distinct species ; 

 but the following description may be considered as applicable 

 to all the specimens hitherto examined. 



The general outline may be considered as elliptical, one ex- 

 tremity being much narrower than the other. This small ex- 

 tremity, for the convenience of description, will be termed the 

 interior extremity. The length varies from one and two- 

 tenths, to one and a half inches. The average thickness about 

 five lines. 



The superior or dorsal surface is divided into two unequal 

 lobes by a longitudinal furrow, in the course of which a raised 

 zigzag line is observed. In fig. 1 . this line is most obvious at 

 the anterior extremity ; in figs. 2. and 3. it is entirely wanting. 



The lobes, with respect to each other, are unequal in extent 

 and thickness. They gradually become thinner towards the 

 circumference, and more particularly towards the posterior ex- 

 tremity. The lobes are marked transversely by 18 — 30 dis- 

 tinct elevated lines or costae, which become more elevated as 

 they approach the raised zigzag line. These costae do not ter- 

 minate at the edges, but are continued at the anterior extremi- 

 ty on the under surface. Faint longitudinal impressions are 

 observed, at unequal distance crossing the transverse costae 

 nearly at right angles. The inequality of the lobes is not always 

 constant: thus, at figs. 1. and 3. the left lobe is the largest; 

 at fig. 2. the largest lobe is on the right. The other lobe of 



