Ran. mono: J^KAcmoi'dHA and ( )sTKACOpA of the Chazv. 245 



The scar has three elements; the large pedicle scar at the apex, a pair 

 of diductors at the sides, and a pair of narrow adductors on a slight 

 ridge in the middle. 



The specimens show considerable variation in the size of the stria^. 

 Some have a comparatively few coarse, direct plications, while others 

 have large stria^ which increase b>- bifurcation and implantation. 



It is very probable that this species is onI>- a local \ariation of 

 Hehertella borealis, as it differs from that species in rather minor par- 

 ticulars. The most persistent differLMice is that the pedicle valve is 

 always convex, while in IT. borealis there is usually a sinus in this 

 valve. 



Locality. — Common at Hawkesbury, Cornwall, and Aylmer, 

 Canada. 



27. Hebertella bellarugosa (Conrad). 



(Plate XXXVI, figures 8, 9.) 



Orthis bellarugosa Con'r.\d, 1843. Proceedings Academy Natural vSciences, Phila- 

 delphia, Vol. I, p. zzi- 



Orthis bellarugosa Hall, 1847. Paleontology New York, \'ol. I, p. 118, PI. 32, fig. 3. 



Hebertella bellarugosa Hall and Clarke, 1892. Paleontology New York, \'ol. \'III, 

 p. 222. 



Orthis {Hebertella.') bellarugosa Winchell and Schuchert, 1893. Paleontology 

 of Minnesota, \'ol. Ill, pt. i, p. 434, PI. 33, figs. 1-4. 



This species is common in the upper part of the lower division of the 

 Chazy at the southern end of Valcour Island, and in the lower part 

 of the upper division on the eastern side. The specimens are of about 

 the same size and have the same characteristics as those found in the 

 Trenton of Minnesota, Wisconsin, and Tennessee. 



Description. 



Shell usually nearly circular in outline, valves about equally convex. 

 Surface marked by from thirty to forty coarse striae which increase 

 by implantation and bifurcation. The radial striee are crossed by 

 sharp concentric lamelhe, producing the rugose appearance which 

 suggested the specific name. From ten to fifteen of the radial striae 

 are stronger than the others, and between each pair of strong striae 

 is a single weaker one, except in the sinus of the brachial valve, where 

 there are two. The pedicle valve is evenly convex, somewhat flattened 

 toward the front, but without a sinus. Hinge line less than the great- 

 est width. Cardinal area not high, nor much incurved. The brachial 

 valve has a narrow median sinus. 



