MODIOLARIA. 



193 



490. 



with dark clicstnut-colorecl shades, folding over the edge. Interior 

 of a briUiant silvery lustre ; edge of the two extreme compartments 

 crenulated, and very strongly so near the ligament ; a few folds on 

 the edge, not corresponding 

 to the external ridges, are 

 found just in front of the lig- 

 ament. Length, one inch ; 

 height, thirteen twentieths of 

 an inch ; breadth, four tenths 

 of an inch. 



Found on Chelsea Beach, 

 and in fishes' maws. Larger 

 specimens are brought from 

 the Newfoundland Banks. 

 Halifax ( Willis) ; Eastport ( Cooper} ; fossil at Montreal {Daw- 

 son). I have two specimens which measure one and one half 

 inches in length, and three fourths of an inch in breadth. 



This species, with M. corrug-ata, is common to the northern 

 coasts of Europe and America, and they are distinguished from all 

 others by the three compartments into which their surface is divided. 

 The distinctive marks between them are particularly pointed out 

 under M. corrugata. The epidermis becomes nearly black by age. 



M. discors (ilf. IcEvigata). 



Modiolaria corrugata. 



Fig. 84. 



Shell oval, tumid, upper edge somewhat compressed and arching, posterior tip 

 somewhat produced and pointed; beaks large, nearly terminal; surface with 

 about sixteen ribs at the anterior third, and very numerous ones at the posterior 

 third. 



Modiola dlscom, Gould, Inv. Mass. 1.30, fig. 84, not of English authors. 

 MijtUas corrugatus, Stimpsox, Shells of New England, 12. 



Shell irregularly oval, tumid, heart-shaped when viewed in front, 

 bhmtly rounded before ; hinge-margin somewhat ascending and a 

 little compressed ; at the termination of the ligament the 

 margin gradually curves downwards, so that the shell is 

 terminated behind by a lobular, somewhat pointed tip on a 

 level with the base ; l)asal margin an undulating curve, 

 nearly parallel with the upper margin ; beaks large and 

 prominent, not in contact, overhanging the anterior extremity ; sur- 

 face as in M. discors; but there are sixteen or more ribs in the 

 13 



Fis. 491. 



