PARYPHORHYNCHUS 191 



PARYPHORHYNCHUS ELONGATUM Weller 

 Plate XXVI, Figs. 10-14 



190b. Paraphorhynchus elongatum Weller, Trans. St. Louis Acad. Sci., 

 vol. 15, p. 216, pi. 1, figs. 1-5. 



Description. Shell of medium size or larger, subovate in outline, longer 

 than wide, the greatest width anterior to the middle, the postero-lateral 

 margins nearly straight or gently convex and meeting at the beak in an 

 acute angle of from 70 to 85 degrees, the anterior and antero-lateral mar- 

 gins rounded. The dimensions of a nearly perfect specimen are: length 

 of pedicle valve 37 mm., length of brachial valve 34.7 mm., width 28.8 mm., 

 thickness 22.5 mm., width of sinus in front 23.8 mm. 



Pedicle valve strongly convex, the greatest convexity near or posterior 

 to the middle, posteriorly the surface is regularly convex transversely in 

 the central portion of the valve, but as it approaches the lateral margins 

 it curves rather abruptly towards the opposite valve and is then continued 

 in a nearly vertical or slightly inflected direction to the edge, from the 

 beak to the front the surface describes nearly a semicircle in full grown 

 shells, but to the antero-lateral margins the curvature is not so great ; the 

 mesial sinus originates near the middle of the valve and is formed rather 

 by the elevation of the borders above the general surface of the valve 

 than by the distinct depression of the sinus itself, it is broad and 

 is gently convex transversely across the depressed portion, anteriorly it 

 is produced as a broad, rounded, lingual extension whose surface at the 

 extreme margin lies at nearly a right angle to the general plane of the 

 valve; the lateral slopes are narrow and are abruptly elevated from the 

 bottom of the sinus in front; the beak is small, sharply pointed, closely 

 incurved and nearly in contact with the umbo of the opposite valve ; the 

 delthyrium is broadly triangular and is nearly filled by the beak of the 

 opposite valve, neither the deltidial plates nor the foramen has been ob- 

 served, but both must be inconspicuous ; the plications originate near the 

 beak and are broad and rounded on top with rounded furrows of about 

 equal width between, they are from ten to fourteen in number, four or 

 five of which occupy the sinus, the outermost plication of the sinus on 

 each side frequently becomes obsolete before it reaches the anterior mar- 

 gin. Internally the teeth are supported by a pair of strong dental lam- 

 ellaa which may extend anteriorly from the beak from one-fifth to one- 

 fourth the length of the valve. Upon the casts of the interior of the 

 valve well defined but delicate pallial sinuses are clearly shown. 



Brachial valve equally or a little more convex than the pedicle, the 

 greatest depth at or near the anterior margin, the surface curving from 

 the anterior margin to the beak, along the median line, with a gradually 

 increasing curvature which becomes rather abrupt near the beak; in the 



