217 



well-marked muscular area occur. The brachial valve is 

 always convex at the beak, below which it becomes flattened 

 or slightly concave, or else continues with more or less uni- 

 form arcuation. Area narrow; cardinal process long and 

 narrow, bifurcated at the tree end. Brachidium consists of 

 loosely coiled spirals, similar to Spirifer. 



Amboccelia umbonata. (Conrad.) (Fig. 125.) (Pal. 

 N. Y., Vol. IV., p. 259, PI. XLIV.) 



Distinguishing Characters. — Plano-convex, almost hemi- 

 spherical contour; strong, distinct and continuous mesial 



r^v 



Fig. 125. Amboccelia umbonata. Dorsal, ventral, profile, and cardinal views of a large 

 and well-preserved specimen of normal form ; interior of a brachial valve enlarged, show- 

 ing muscular impressions, sockets, etc. ; interior of pedicle valve enlarged, showing area, 

 delthyrium, teeth, etc. ; mold of interior, with spiral brachidium embedded in it, enlarged 

 (from Hall). 



sinus in the pedicle valve, which is very gibbous ; semi-ellip- 

 tical brachial valve, which is faintly convex at the umbo, 

 and concave below the middle and at the sides; shell slightly 

 wider than long. 



Found in the Moscow shales (very rare in the upper, but 

 common in the lower two or three feet, extremely abundant 

 in the lower foot), at Sections 4 and 5; Encrinal limestone, 

 at Section 5 (rare) ; Lower shales, at Sections 5 to 8, and on 

 the Lake Shore (more or less abundant throughout) ; Transi- 

 tion shales, on the Lake Shore (frequent) ; Marcellus shale, 

 in Bay View Cliff (not uncommon). 



Amboccelia nana. Grabau. (Fig. 126.) (1898: Ambocoe- 

 lia umbonata, var. nana. Grabau. Report of N. Y. State 



