38 -"iiig- F- Focrste 



wise compara:ively flat surface. Each of these grooves is formed 

 by a series of pits distinctly smaller than those on the anterior 

 half of the shell. The distance from the beak at which the 

 arrangement of pits in comparatively distant rows gradually 

 merges into the arrangement in closely contiguous rows varies in 

 different specimens. In some specimens, the rows become con- 

 tiguous within 8 mm. from the beak ; in others they remain distant 

 even at 13 mm. from the beak. The type, figured by Hall and 

 Clarke, was only a young specimen. 



The type was found in the Saltillo limestone at Clifton, Ten- 

 nessee, a short distance south of the Landing. Similar specimens 

 occur in the Logana limestone at Frankfort, Kentucky. Both of 

 these horizons are regarded as identical with the Hermitage of the 

 area covered by the Columbia folio, in Tennessee. 



Trcmatis ottazvacnsis, Billings is figured as having rows of 

 pits in close juxtaposition even in the umbonal area toward the 

 beak. There is no indication of flat interspaces on the posterior 

 half of the shell. Shells of this type, I have not seen either in 

 Kentucky or in Tennessee. 



Trematis fragilis, Ulrich. 



(Plate V, tigs. 3, 4, 2.) 



Trcmahs fragilis was described by Ulrich from the lowest 

 beds of the Cincinnati group, a few miles south of Covington, on 

 Bank Lick creek, Kentucky. According to Nickles, this places 

 its horizon in the strata beneath the Fulton layer, in the argillaceous 

 strata near the base of the section. Its chief characteristic is the 

 limitation of the radiate lines of minute pits to the posterior part 

 of the shell, chiefly posterior to a line crossing the shell transversely 

 at the beak, although, in case of the pedicel valve, these rows of 

 pits may be detected also for a short distance anterior to the 

 foramen. These pits are too small to be detected without the aid 

 of a lens. The shell, in general, appears smooth, modified in the 

 case of the upper valve by wrinkles, some of them concentric, which 

 may be due in part to vertical compression of the shell which 

 usually is preserved in an argillaceous matrix. The shell of both 

 valves is very thin, and the traces of original concentric markings 

 usually are faint. The outline of the shell is nearly circular, 

 slightly wider than long, and the upper vahe is only moderately 



