Silurian Fossils. 17 



extending- as far as the beak. On each side there is a single, 

 much less distinct lateral plication. Beyond this, there is 

 room for an additional plication, but this area is smooth. The 

 sinus of the pedicel valve is distinct as far as the beak, and 

 the limiting plications may be traced the same distance. Be- 

 yond the latter, there is a much less distinct plication, disap- 

 pearing posteriorly. The surface does not preserve any indi- 

 cation of strise, but may not be fine grained enough to preserve 

 them. 



West Union Bed, at Harin Hill, four miles west of \^alley, 

 in Lewis county, Kentucky. 



The presence of distinct dental plates in the casts of this 

 species separates it from Reticnlaria, entirely aside from the 

 fact that no evidence of strong fimbriate concentric striae has 

 been discovered. It appears to belong to the Spirifcr vaimx- 

 cmi type of shells. Spirifcr simples is a distinctly more glo- 

 bose, and more strongly plicate shell. 



Spirifer exiguus, sp. nov. 

 Plate I, Figs. 8, A, B, C. 



Shell small. The largest specimiCn found so far equals 

 9 mm. in length. 10 mm. in width, and 6 A mm. in thickness : 

 the length of the brachial valve is 8 mm. and the width of the 

 median fold at the anterior margin is 3 mm. The brachial 

 valve is moderately convex. The median fold is low and 

 broad, but is distinctly defined on each side by the limiting 

 grooves ; anteriorly it is flattened, with occasionally a very 

 faint trace of a median depression. Lateral plications four, 

 usually faint, the first occasionally distinctly broader than the 

 rest, the second still fairly discernible, the last two almost 

 obsolete. ^ledian groove of the pedicel valve shallow, not 

 angular or narrow ; the limiting plications are distinctly more 

 conspicuous than the lateral plications, being both broader and 

 more elevated. Lateral plications faint, four in number, the 

 last two almost obsolete. Hinge area rather low. Beak of 

 the pedicel valve strongly incurved but not extending beyond 



17 



