Silurian Fossils. 27 



Orchard clays and limestones. Above this horizon, in the 

 states mentioned, is it a rare fossil. 



One mile south of Carrs, in Lewis county. Kentucky, a 

 single specimen with three plications on the fold, and with 

 five lateral plications was found, probably in the West Union 

 bed. This is similar to the form called Platystrophia dayton- 

 cusis. 



Dalmaxella elegaxtula, DaUnan. 



Small, poorly preserved specimens, Jr.o mm. in length, are 

 found in the West Union bed at Harin Hill, 4 miles west of 

 Valley, in Lewis county, Kentucky. 



Another small variety occurs at both the George W. Def- 

 enbaugh and the Traction quarry, in Kokomo, Indiana. 



Rhipidomella magxicardixalis. sp. nov. 

 Plate I, Figs. 11 A-D ; Plate II. Figs. 12 \, B. 



Shell with a length of 12 mm., a width of 15 mm., and a 

 depth of 9 mm. Both valves evenly and rather strongly con- 

 vex. Hinge line distinctly shorter than the width across the 

 middle of the shell. Postero-lateral angles rounded. Gen- 

 eral outline of the shell nearly circular. Radiating striae 

 rather coarse, about 10 or 11 in a width of 5 mm. along the 

 antero-lateral margin, less numerous directly in front. ^lus- 

 cular area of the pedicel valve deeply impressed, tiabelliform. 

 occupying about half the length of the shell. Dental plates 

 short but strong. Crural plates of the brachial valve strong, 

 divergent, pointed, separated by a strong cardinal process 

 which begins a short distance anterior to the bases of the 

 crural plates, and extends back for a length of fully -1 mm. 

 For half its length it projects as a strong process beyond the 

 cardinal area of the brachial valve into the space beneath the 

 beak of the pedicel valve. At the tip the process becomes 

 broader than at mid-length, and apparently is supplied with 

 three vertical ridges. Owing to the preservation of the shell 

 in the form of casts, it has been impossible to decipher a 

 part of its structure, but the deeply impressed muscular area 



27 



