236 Annals of the Carnegie Museum. 



a species which is exceedingly abundant in the lower part of the Chazy 

 at Chazy, New York. 



A third specimen sent by Dr. Hovey, and presumably labeled by 

 Hall, proves to be a large exfoliated brachial valve of Ilehertclla vul- 

 garis. 



To return to the first specimen, which must be taken as the holotype 

 of Orthis costalis. This specimen is on a chip of dark limestone which 

 contains no other fossil except a fragment of a Strophomena. The litho- 

 logical character of the fragment is entirely different from that of the 

 other two fragments sent by Dr. Hovey, and is a pure dark limestone 

 such as is found at Chazy only in the Middle Chazy or the Black River. 

 The strata of the Lower Chazy at Chazy are all yellowish in tone. 

 The specimen is imperfect, but it agrees in proportions and number of 

 plications with Orthis tricenaria, and it is possible that it is a specimen 

 of that species. The writer has described two species of Orthis from 

 the Chazy, but both are quite different from this type of Orthis costalis. 

 Orthis acutiplicata comes from the lower layers of the Chazy at Valcour 

 Island, but it has only about half as many plications as 0. costalis. 

 Orthis ignicida is more like 0. costalis, but the width at the hinge equals, 

 or is greater than, the width below, and the shell is nearly one-third 

 wider than long (10X14 mm. in one specimen, 4X6 mm. in another, 

 and 9.5X14 in a third). Orthis costalis and 0. tricenaria are long and 

 have the width at the hinge less than the greatest width, while Orthis 

 disparalis and 0. igniciila are short and wide, and the greatest width 

 is at the hinge. 



19. Orthis ignicula Raymond. 



(Plate XXXV, figures 5-7.) 

 Orthis disparalis Billings, 1859. Canadian Naturalist and Geologist, Vol. I\', 



p. 440, figs. 20a, h (non Conrad). 

 Orthis ignicida R.wmond, 1905. American Journal of Science, series 4, Vol. XX, 



P- 369. 



Description. 

 Shell transversely oval in outline, wider than long. Greatest width 

 at the hinge. Pedicle valve strongly convex, the cardinal area high 

 and a little incurved. Brachial valve nearly flat, with a broad de- 

 pression toward the front. Cardinal area of this valve also wide. 

 Cardinal process small. Delthyrium narrow, the deltidium not 

 preserved in any of the specimens at hand. Surface marked by from 



