NATURAL SCIENCES OF PHILADELPHIA. 413 



This species differs from P. elongata, Goldf. (Petref. Germ. ii. 135, Taf. cxix. 

 5), in having a much smaller body, and less distinct from the alate extrem- 

 ities. 



Mytilus, Linnaeus. 



Mytilus Whitfieldianus, n. sp. Shell small, ventricose, transversely elon- 

 gate, very oblique, with terminal beaks. Hinge line two-thirds the length of 

 the shell, forming a rounded, very obtuse angle with the somewhat circular 

 posterior border ; ventral border slightly arcuate, more rapidly curved beneath 

 the beaks. Greatest width opposite the posterior extremity of the hinge-line. 

 Umbonal ridge elevated, crowded over towards the hinge line, and rendered 

 somewhat angular, more sharply so towards the beak. Surface of shell and 

 cast marked by numerous concentric lamellose lines. One of the best preserved 

 specimens shows distinctly a multitude of minute diverging striae running in 

 all parts of the surface at right angles with the lines of growth. 



Length from beak to posterior extremity *59 (100) ; greatest height *29 (50) ; 

 length from beak to extremity of hinge line *44 (75) ; convexity of right 

 valve -12 (20). 



localities. Holland, Ottawa county and Marshall. 



Cakdinia, Agassiz. 



Cardinia complanata, n. sp. Shell of moderate size, ovoid, compressed, 

 with sub-central beaks. Ventral border gradually curved to the abruptly 

 turned extremities, from which the outline is nearly straight along the cardi- 

 nal slopes to the obtuse incurved beaks ; line joining extremities equidistant 

 from beaks and ventral margins. Right valve flattened, producing an angular 

 fold along the postero-dorsal declivity near tbe hinge line. Exterior sculp- 

 tured by about 20 broad regular furrows parallel with the ventral border. 

 Other characters unknown. 



Length 1*2 (100) ; height # 64 (53) ; length of anterior cardinal slope to ex- 

 tremity of shell "64 (53) ; of posterior *S7 (72) ; convexity of right valve 

 (perhaps mechanically compressed) -13 (11). 



Locality. Union, in Branch county, in blue argillaceous shales of the Hu- 

 ron group. 



Cardinia ^equimarginalis, n. sp. Shell of medium size, tumid, beaks cen- 

 tral, anterior and posterior hinge-slopes at right angles with each other, 

 straight, very nearly equal and symmetrical ; extremities rounded, situated 

 about midway between beaks and ventral margin, which is regularly arcuate 

 between the extremities ; posterior extremity a little more acute than the an- 

 terior. Shell tumid, regularly convex, slightly truncate along the antero-car- 

 dinal slope. Beak (of cast) marked only by obscure incremental lines and 

 nearly obsolete concentric furrows. Hins;e structure unknown. 



Length of shell -91 (100) ; height -86 (94) ; thickness -50 (55.) 



Localily. Marshall. 



Cardinia robusta, J. de C. Sowerby is a close representative of this species, 

 but is not so high, and is more produced and angulated posteriorly. 



Cardinia concentrica, n. sp. Shell of medium size, ventricose, transverse- 

 ly elliptic, with subequal extremities and marked ventral enrolment. Beaks 

 appressed, incurved, rising little above the hinge, distant one-fourth the shell- 

 length from the anterior end ; umbo and middle of the shell flattened antero- 

 posterior^ ; antumbonal ridge inflected towards the hinge, forming above a 

 lunuliform area ; dorsal and ventral borders sub-parallel in the adult shell ; 

 posterior end obtusely, or at length truncately rounded ; anterior end para- 

 boloid. Hinge line straight and rather extended posteriorly. A broad shal- 

 low inconspicuous sinus extends from the posterior ventral margin towards 

 the beak. External surface marked, towards the beak, with remote, equidis- 

 tant, raised, concentric striae and intervening flat belts ; towards the margin 



1862.] 



