FOSSILS OF THE CLINTON GROUP. 569 



shows a fairly low linear but distinct or moderately triangular cardinal 

 process flanked on either side by a diverging linear ridge, and these are 

 flanked in turn on the exterior side by a much larger linear ridge, the 

 crural plate, the extension of which antero-laterally serves to give a dis- 

 tinct outline to the more posterior parts of the muscular area, which an- 

 teriorly shows no outlines in our specimens. A broad median low ridge 

 starts from the cardinal process but soon disappears anteriorly. 



This shell is found at Fauver's Quarry, Soldiers' Home, Huffman's 

 Quarry, Fair Haven, Ohio, and apparently at Hanover, Indiana. 



Strophomena {Strop honella) patenta, Hall. 



(Plate 27, Figs. 35, 36, 37, young- specimens.) 



The shell begins its existence with the pedicle valve convex and the 

 brachial concave. Later the anterior and lateral margins of the pedicle 

 valve become concave or turned up, and those of the brachial valve con- 

 vex or turned down. This is likewise true of Strop honella {Amphisiro- 

 phia) stria a. In spite of the abundance of this shell in the Clinton of 

 Ohio and Indiana, no interiors have yet been found, nor has a clear hinge 

 area been seen. By digging away the shell from its matrix in case of the 

 pedicle valve, it was found that the postero-lateral angles were well de- 

 fined, owing to a sort of low ridge running from the usual position of the 

 teeth antero-laterally, the ridges on either side of the muscular area 

 presenting a concave outline for a short distance near the beak and alter 

 that being strongly divergent. These ridges in our rather unsuccessfully 

 cleaned specimens can usually not be traced more than 5 mm., hence the 

 general form of the muscular area must remain undetermined, but it seemed 

 to us that as far as it extended it showed rather strongly typical stro- 

 phomenoid characters. In one specimen, 15 mm. long, the ridges were 

 seen to curve forward and a little inward before they disappeared, while 

 not leaving the slightest trace anteriorly. In this they resemble the 

 degree of distinctness of outline of the muscular area in Str. striata, but the 

 included area is relatively somewhat broader. A low median elevation 

 seen near the beak soon disappears entirely, but not before showing in 

 some specimens at. least a fine median groove, which begins a short dis- 

 tance anterior to the beak and also soon disappears. 



The exterior of the shell is marked by numerous fine radiating plr 

 ations or rather striae. These are intercalated so frequently and develop, 

 in size so gradually anteriorly that the earlier started plications are of 

 larger size, and are more prominent than those successively later in origin, 

 so that anteriorly the shell shows stronger striae at more or less regular 

 intervals among the finer striae. Very fine concentric striae of growth 

 cover the entire shell. At Fauver's Quarry occur specimens in which 

 the radiating striae are rather more equal in size and are rather larger 



