Rav.monu : Braciiioi'oda and OsiKAtoDA oi' inF, Chazv. 243 



t 



pedicle \alvc, while others ha\e that \alve evenly convex, or merely 

 flattened toward the front. The brachial valve usually shows a narrow 

 but not deep sinus, which extends from the beak nearly or cpiite to 

 the front. The line in which the two \alves meet is usually straight, 

 but in those specimens which ha\e a sinus in the pedicle valve and 

 none in tlic brachial, the frt)nt is sinuate. Mature specimens usually 

 have from sixty to ninet\' hue striie on each valve. The stria? increase 

 both by bifurcation and implantation. 



The cardinal area of the pedicle \al\e is high and sliiihth- incurved, 

 the delthyrium apparently open. The teeth are supported by thin 

 lamellse, between which are the scars of the muscles. In the brachial 



17 18 



Fig. 17. Hehertella vulgaris Raymond. Two brachial valves. One-half 

 larger than natural size. 



Fig. 18. The same species. The interior of two pedicle valves. Same mag- 

 nification. 



\al\e there is a low median septum which expands at the posterior 

 end, forming a platform, in the middle of which is the small linear 

 cardinal process. In front of this platform are two pairs of deep ad- 

 ductor scars. The dental sockets are narrow and deep. 



Locality.- — -This species is common at Chazy and Valcour Island, 

 New York, and occurs at many different horizons, but is commonest 

 in the upper di\ision. 



26. Hebertella imperator (Billings). 



(Plate XXXVI, figures 6, 7-) 

 Orlhis imperator Billings, 1859. Canadian Naturalist and Geologist, \'oI. IV, 



p. 435, figs. 11-13. 

 Orlhis imperalor Billings, 1863 Geology of Canada, p. 129, fig. 55. 

 Heberlella imperalor H.\ll and Clarke, 1892. Paleontology of New York, Vol. 



\'I1I, pt. I, p. 222. 



This species, the individuals of which attain a larger size than any 

 of the other Orlhidcc of the Chazy, does not appear to occur in the typical 

 Chazy deposits, but is very abundant in the Ottawa Valley. It 



