234 



Fig. 145. Leiorhynchus dubium. A specimen without fold in brachial valve: dorsal, 

 ventral, and profile views of a more strongly marked individual (from Hall). 



twenty-four to twentv-six slender, rounded surface plica- 

 tions, of which about six are on the fold. 



A specimen from Section 7. seventeen to twenty-one feet 

 b (low the Encrinal limestone, appears to be of this species. 



Genus CENTKONELLA. Billings. 



[Ety. : A little point.] 



(1859: Canadian Naturalist and Geologist, Vol. IV., p. 131. 1893: Pal. 

 N. Y.. Vol. VIII. , Pt. II., p. '265.) 



Shell plano-convex or concavo-convex, with a terebratu- 

 loid outline. The beak of the pedicle valve is acute and in- 

 curved, with ;i terminal foramen, which is continuous with a 

 partially-closed delthyrium. The brachial valve bears a 

 median sinus, while the center of the pedicle valve is angular, 

 the sides sloping off rapidly. The brachidium consists of two 

 branches, which unite medially to a triangular plate bear- 

 ing a median ridge. 



Centronella impressa. Hall. (Fig. 146.) (Pal. N. V.. 

 Vol. IV.. p. 402, PI. LXI.) 



Distinguishing Characters — Sub-ovate outline ; convex 

 angular pedicle valve, the longitudinal outline of which is 



i 



146 Centronella impressa. Dorsal, ventral, and profile views of a full-grown 

 specimen of ordinary si/>- : interior of a brachial valve, showing the cardinal process and 

 strong callosities to which the crura are attached. 



slightly arched; beak truncated by the foramen; small 

 brachial valve, flattened or sometimes sharply depressed 

 along the center, with the front produced and curved 



