MYTILACEA. MOLLUSCA. MODIOLA. 129 



MODI^OLA DI'SCREPANS. 



Shell suh-oval^ broadest behind; beaks nearly terminal: hinder 

 extremity sonieiohat lobed ; surface divided into three compart- 

 ments, of which, the anterior is marked by about eight, and the 

 posterior by numerous radiating lines, epidermis olivaceous. 



Figure 83. 

 Slate Coll., No. 157. Soc. Cab., No. 2345. 



My'tilus discrepans, Montagu; Test. Brit., p. 1G9, and Suppl., 65. pi. 2f), f. 4. 



Maton and Rackett; Lin. Trans., viii. pi. 3, f. 9. Pennant ; Brit. ZooL, iv. 



241. Dillwvn; Catal, 319. Turton : Biit. Biv., 202. Conch. Diet., 112. 



Fleming ; Brit, .^nim., 413. Wood ;. Index, pi. 12, f. 38. 

 My'tilus discors, O. Fabr. : Fauna Granl., 191. Chemn.; Conch., viii. 191, 



t. 86, f. 767. (var ) 

 Modiola ls2vig;Ma, (var.) Gray; Jip-pendix to Parry's 2d Voyage. 



Shell somewhat oval, rather oblique, highest about the middle, 

 rounded before, base slightly curved, hinge margin straight and 

 then curving obliquely downward ; beaks near the anterior end, 

 prominent, and rounded ; valves moderately convex ; surface 

 coarsely marked by the lines of growth, and divided into three 

 fan-shaped compartments, of which the foremost one is marked 

 by about eight small, rounded, rib-like ridges, the spaces between 

 them being flat, the hinder one by numerous similar ridges, and 

 the central one is plain, or with very minute radiating lines ; the 

 limits between the posterior and middle compartments are desig- 

 nated by an elevated ridge passing from the beaks, and here the 

 basal margin of the posterior compartments projects abruptly be- 

 yond that of the middle one, so that the rounded point of the shell 

 forms a projecting lobe. Epidermis olive-green with dark chest- 

 nut-colored shades, folding over the edge. Interior of a brilliant 

 silvery lustre ; edge of the two extreme compartments crenulated, 

 and very strongly near the ligament ; a few folds on the edge, not 

 corresponding to the external ridges, are found just in front of the 

 ligament. Length J inch, height i|- inch, breadth ^V inch. 



Found on Chelsea Beach, and in fishes' maws. Larger speci- 

 mens are brought from the Newfoundland Banks. I have two 

 specimens which measure 1^ inch in length, | inch in breadth. 

 17 



