Silurian Fossils. 15 



extending one or two millimeters farther. The crural plates 

 of the brachial valve are short, nearly vertical, and only mode- 

 rately divergent ; there is no distinct median septnm in this 

 valve. In the type specimen there are about eleven radiating 

 striae in a width of 5 mm. at a distance of 17 mm. from the 

 beak of the brachial valve, but in some specimens the number 

 of striae is greater, so that the smaller number of radiating 

 striae seen in the type specimen does not seem to be a constant 

 feature. The anterior of the shell is deflected so as to indicate 

 the relationship of this form to shells with a distinct sinus 

 and fold. 



West Union bed, at the spring on Big Salt Lick creek, one 

 mile souti of Glen Springs, on the road to Xoah, in Lewis 

 county, Kentucky. 



The sharp median septum of the pedicel valve has not been 

 noted in typical forms of Spirifcr radiatus. The beak appears 

 to be somewhat less incurved. The most conspicuous differ- 

 ence, however, is the absence of a distinct median sinus, giving 

 the pedicel valve a more evenly convex surface. 



Spirifer nanus, sp. nov. 

 Plate I, Fig. 7 ; Plate IL Fig. 7. 



Shell apparently small, the largest specimens found not 

 exceeding 10 mm. in length, 11 or 12 mm. in width, and 4 mm. 

 in convexity. Considering the size of the shell, the brachial 

 valve is strongly convex, especially along the median fold. 

 Only the internal casts of the brachial valve have been found 

 so far, and these show the presence of the crural ridges, about 

 2 mm. in length, and also a faint median septal striation, about 

 5 mm. in length. If our interpretation of the shell be correct, 

 it may be related to the form represented by figures 14 to 18 

 on plate 21, Volume VIII, of the New York Paleontology. 

 In our specimens, however, the median fold is less distinctly 

 limited, especially toward the beak, where it is but slightly 

 elevated above the general convexity of the shell. There are 

 no traces of radiating striae on these casts. 



15 



