ALLORHYNCHUS 199 



extremely fine, crowded concentric striae can be detected. Occasionally 

 stronger lines of growth are present, but they are never conspicuous. 

 Horizon. Kinderhook. 



ALLORHYNCHUS MACRA (Hall) 

 Plate XXV, Figs. 1-6 



1856. Bhynchonella niacra Hall, Trans. Albany Inst., vol. 4, p. 11. 

 1856. Rhynchonella ricinula Hall, Trans. Albany Inst., vol. 4, p. 9. 

 3882. Rhynchonella macra Whitfield, Bull. Am. Mus. Nat. Hist., vol. 1, 

 p. 52, pi. 6, figs. 40-42. 



1882. Rynchonella ricinula Whitfield, Bull. Am. Mus. Nat. Hist., vol. 1, 



p. 53, pi. 6, fig. 46. 



1883. Rynchonella. macra Hall, 12th Ann. Rep. Geol. Surv. Ind., p. 334 



pi. 29, figs. 40-42. 

 1883. Rynchonella ricinula Hall, 12th Ann. Rep. Geol. Surv. Ind., p. 330, 



pi. 29, fig. 46. 

 1906. Rhyn-chonella macra Beede, 30th Ann. Rep. Geol. Surv. Ind., p. 



1307, pi. 22, figs. 40-42. 



1906. Rynchonella ricinula Beede, 30th Ann. Rep. Geol. Surv. Ind., p. 



1308, pi. 22, fig. 46. 



1910. Allorhynchus macra Weller, Bull. Geol. Soc. Am., vol 21, p. 509, 

 %. 9. 



Description. Shell small, compressed, subovate to subtriangular in 

 outline, usually a little wider than long but sometimes longer than wide, 

 especially in small or young individuals, the greatest width anterior to the 

 middle, the postero-lateral margins gently convex or nearly straight and 

 usually meeting at the beak in an angle of less than 90 degrees, the 

 antero-lateral and anterior margins regularly rounded or with the an- 

 terior margin sometimes straightened. The dimensions of two individuals 

 are: length 6.5 mm. and 5.5 mm., width 7.1 mm. and 6 mm., thickness 3 

 mm. and 2.7 mm., width of sinus in front 4.5 mm. and 3.1 mm. 



Pedicle valve most convex posterior to the middle, the surface gently 

 arched from beak to front and also transversely along the line of greatest 

 width, but posteriorly the curvature to the lateral margins is more 

 abrupt, towards the beak the edge of the shell along the postero-lateral 

 margins is abruptly and sharply inflected to form a rather conspicuous 

 pseudo-cardinal area; mesial sinus entirely obsolete posteriorly where it 

 is replaced by a slight mesial elevation which is not differentiated later- 

 ally from the lateral slopes of the valve, towards the front the mesial 

 portion of the valve is somewhat flattened and is rarely slightly de- 

 pressed in a broad, shallow, ill-defined sinus ; the beak is pointed, scarcely 

 incurved and is produced posteriorly rather conspicuously in a nearly 

 horizontal direction ; the delthyrium is broadly triangular and is partially 

 closed by deltidial plates which are pierced at the apex by a subelliptical 

 foramen which encroaches to some extent upon the beak of the valve; 



