Siiburban Geology of Richmond, Indiana. 



293 



similitude of a small Unio f and another, by no means common, 

 having inequilateral valves marked with delicate concentric lines. 

 Except these anonymous ones, and the Strophomena Fig. 8. 



semiovalis, /3. deltoidea, and Orthis testudinaria, 

 these shells are very common. The Pterinea is 

 chiefly found in the "marlite;" and indeed, this 

 bed is most prolific of the genera. On breaking 

 open these bivalves we often find them filled with 

 calcareous spar ; even the thin Strophomenee are 

 generally compacted in the same manner. 



Univalves. — One species of Turbo, (Monodon- 

 ta?) and this is not common; one species of Tur- 

 ritella, which is still less frequently found ; a sin- 

 gle specimen of a large Conularia quadrisulcata ; 

 five species of Orthoceratites ; the Platyceras ven- 

 tricosum (Conrad;) a Bellerophon, and a fossil 

 which I venture to place here, and call for present 

 convenience, Aulacera. Of these, the Orthocera- 

 tites is much the most common. The largest spe- 

 cies I have always found in the "marlite;" one 

 specimen, which as usual is not perfect, is upwards 

 of two feet long, and another eighteen inches long ; 

 some have a diameter of but one fourth of an inch, 

 while the larger ones, which instead of being cylin- 

 drical are elliptical, have a long diameter of five 

 inches and a transverse diameter of three inches. 

 The siphuncle of these large specimens is lateral, 

 and varies from two to two and a half inches in 

 diameter. 



Insulated as I am with respect to the seats of 

 science, and inaccessible to me as are the appro- 

 priate authorities, I do not know whether the fossil 

 I am about to describe is already familiar to the 

 paleontologist, or whether it is altogether unique ; 

 but as none of my scientific friends, who on visit- 

 ing this place, have seen it, and none who have 

 received casts of it appear to have been acquainted 



I say Unio by way of comparison ; I do not suppose it to be a fresh-water shell. 



