PRODUCTELL^ OF THE CHEMUNG GROUP. 173 



The interior of the valve is finely papillose and papillose-striate, so 

 that some of the casts have a minutely interruptedly-striate surface. 

 The cast of the ventral valve preserves irregular and somewhat elongate 

 semioval imprints of the occlusor muscles, and the impressions of the 

 divaricator muscles are deeply striated, "wide spreading, reaching the 

 inner margin of the wings, and extending for more than one-third the 

 length of the valve. The cardinal process of the dorsal valve is bilobed 

 in the middle, and each lobe is again divided, leaving a quadruple imprint 

 on the stone. 



This shell is subject to much variation in the convexity of the ventral 

 valve, and also in the distribution of the spiniferous tubercles. The larger 

 number of specimens are ventricose, a little flattened and rarely depres- 

 sed along the middle. 



Mr. Conrad has described the ventral valve of S. lachrymosa as " ventricose, 

 " depressed towards the hinge-extremities ; disc slightly flattened in the mid- 

 " die, marked with numerous elongated tubercles arranged in radii which 

 " profoundly bifurcate ; hinge-line not salient at the extremities, angulated, 

 " sab-margin with prominent tubercles ; umbo ventricose; summit above the 

 " cardinal line. Locality : Chemung-narrows, New-York, Devonian- shale." 



The specimens in my collections from the Chemung-narrows are usually not 

 extremely ventricose, and the spiniferous tubercles are more elongate than in 

 most other species in the collection, sometimes becoming costae towards the 

 front of the shell. This feature is shown in some of the figures on Plate xxv, 

 while other figures illustrate the prevailing forms of those which I have referred to 

 this species from Cattaraugus county and farther west. 



Notwithstanding the variable character of the species, it is for the most part 

 readily recognized among the others of the group ; and it certainly has no very 

 close resemblance to any of the forms in the Corniferous limestone or Hamilton 

 group. 



The casts show faint indications of an area, and of teeth in the ventral valve ; 

 but teeth-sockets are not visible in the dorsal valves of any specimens I have 

 thus far examined. 



Geological formation and localities. In the Chemung group, near Factoryville 

 and Chemung-narrows, Chemung county ; at Painted-post, and. near Bath in Steu- 

 ben county; near Conewango and Randolph in Cattaraugus cotinty, and near 

 Ellington in Chautauqua county. 



