164 NEW YORK STATE MUSEUM 



largely by interpolation in the older part of the shell and by splitting 

 in the anterior portion. Ten or 12 spines are scattered over the sur- 

 face of the shell and 

 several crowded on 

 the ears. Posterior 

 part of the valve 

 marked with concen- 

 tric wrinkles becom- 

 ing stronger near the 

 ears. The interior of 

 T, J . . r • ^ , ^ the valve has the 



Jrroductus tenuicostiiormis nov. Cape le Trou, 



Grindstone I. muscular attachments 



well developed and sharply defined as is revealed in a cast; anterior 

 adductors attached to low indistinct ridges ; diductors attached to 

 four or five low bilobate or looped ridges on either side of the ad- 

 ductors. Brachial valve more nearly subquadrate than the pedicle 

 valve, the hinge being about equal to the anterior width of the shell. 

 Valve nearly flat over the visceral region, somewhat depressed in the 

 central region and elevated around it, geniculated at the margin (un- 

 less surrounded by a wall). Beginning at the ears a very narrow 

 platform extends outward enlarging as it passes around the sides to 

 the anterior of the valve where it has the width of a millimeter or 

 more. Mesial septum reaching well toward anterior part of valve. 

 Adductor attachments nearly round but showing a tendency to digi- 

 tate lobation. Cardinal process bilobate at least below, as shown in 

 cast. 



Dimensions. Length of shell, 14 mm; width, 18 mm; length of 

 hinge, 19 mm ; 9 or 10 striae in 5 mm. 



Remarks. The horizontal platform surrounding the visceral area 

 of the brachial valve is of unusual interest since it occupies the posi- 

 tion of the murication in Marginifera. No murication is, however, 

 preserved in our specimens, though it could hardly be expected that 

 it would be, and there is little to lead one to suspect that such muri- 

 cation did exist. The generic disposition of the shell is not quite 

 clear. The cardinal process is bilobate, below at least, as in Pro- 

 ductella, though there seem to be no crural plates to assist in forming 

 sockets for the teeth of the opposite valve and the pedicle valve 

 seems not to have had teeth. The well-defined muscular 

 attachments go with other characters in suggesting its place in Pro- 

 ductus. The platform, even though not supporting a murication, 

 seems to forecast the subgenus Marginifera. Since the more 

 important features are those of Productus, it seems advisable to 



