Cincinnatian and Lexington Fossils 45 



width at the hinge-Hne. In addition to Rafinesquina dedivis, the 

 rock at Boyd's station contains Ccratopsis intcvniedia, Ulrich. 



Leptaena tenuistriata, Sowerby. 



The following description of Leptaena tenuistriata was pub- 

 lished by Sowerby in Mnrchison's Silurian System, vol. 2, p. 636, 

 and illustrated by figure 23. on plate 22, in 1839: 



Semicylindrical, closely striated; top of the upper (pedicel) valve with 

 12 or more concentric rugae, convex ; sides expanded. 



A shell much resembling L. depressa, and about the same size, but orna- 

 mented with much closer striae and of a thinner substance. 



Locality — Marloes Bay; Narbeth, Pembrokeshire; also at Gaerfawr in the 

 Caradoc Sandstone of Montgomeryshire. 



In the accompanying figure, 14 radiating striae are figured as 

 occupying a width of 4 mm. The shell, viewed from above, is 

 rather quadrate in appearance, the concentric wrinkles approaching 

 the hinge-line nearly at right angles, and there being no conspicuous 

 extension of the shell along the hinge-line. The main body of the 

 pedicel valve is comparatively flat, the geniculate border bending 

 abruptly downward. The concentric wrinkles are well defined. 



In Leptaena richmondensis (this Bulletin, vol. xiv, plate iv, 

 figs. 10 A,B), from the Richmond of Ohio, Indiana, and Ken- 

 tucky, identified by Hall as Leptaena tenuistriata, the number of 

 radiating striae often is only 9 in a widdi of 4 mm., the shell is 

 shorter, and is conspicuously elongated along the hinge-line, the 

 width frequently equalling twice the length. Moreover, the down- 

 ward flexure of the geniculate border is less abrupt. The radiating- 

 striae are broad, separated by sharp, narrow grooves, and resemble 

 pieces of cord in close juxtaposition. 



In the Saltillo bed, at Clifton, Tennessee, a single small valve 

 of a Leptaena was found (plate v, figs. 9 A.B), which resembles 

 Leptaena tennistriata in having 14 radiating striations in a' width 

 of 4 mm. These striae are rather sharp, and are separated by 

 grooves equal in width to the striae. The concentric wrinkles are 

 only moderately conspicuous. The body of the pedicel valve is 

 comparatively flat, and the flexure at the comparatively short 

 geniculate border is fairly abrupt. The shell is relatively shorter 

 and broader than in the figure of the type specimen. Its length 

 is about 1 1.5 mm., and its width, i8mm. While not identical with 

 Leptaena tenuistriata, from the Caradoc of England, it probably 



