BRACHIOPODA. 
231 
relationship to Clitambonites, as does also the concave plate in the delthyrium 
of Protorthis Like Protorthis, this genus includes a series of primordial 
species antedating both Orthis and Clitambonites, but apparently having 
attained about the same stage in the line of development toward these genera. 
To the species above mentioned may probably be added the Streptorhynchu-s ? 
primordiale, Whitfield,* from the Calciferous beds at Fort Cassin, and Orthisina 
grandma, Billings,f from the Chazy. 
In the lower beds of the Upper Silurian of the Anticosti series occurs the 
Orthis ? laurentina, Billings, a shell with the interior characters, and the exterior 
expression of Orthis calligramma, differing only in the presence of deltidia upon 
both valves, and in this respect resembling Billingsella and Clitambonites. 
Genus PROTORTHIS, gen. nov. 
PLATE vn A, FIGS. U-21. 
1868. Orthis, Hartt. Dawson’s Acadian Geology, Second Edition, p. 644, fig. 283. 
1884. Orthis, Walcott. Bulletin No. 10, U. S. Geological Survey, p. 17, pi. i, figs. 1, 1 a-d. 
? 1884. Oi'this, Walcott. Monogr. U. S. Geological Survey, vol. viii, p. 22, pi. ix, figs. 8, 8 a. 
1886. Orthis, Matthew. Transactions Royal Society of Canada, Sec. IV, p. 43, pi. v, figs. 20 a-c; 
(?) p. 42, pi. v, figs. 18 a-c. 
There is a small group of shells passing under the name of Orthis which 
should be separated from that genus, and given a new designation, since none 
of the existing generic groups can properly receive them. Their distinctive 
characters are as follows: 
Diagnosis. Shells' small, transversely subquadrate or semicircular. Hinge¬ 
line straight, its length being equal to the greatest width of the valves. Yalves 
unequally biconvex, or sub-planoconvex, the pedicle-valve being the larger. 
The cardinal area is narrow on both valves, but is higher on the pedicle-valve, 
and is transected by a broad delthyrium which is closed below by a concave 
plate apparently produced by the union of the dental lamellae, which are not 
continued to the bottom of the valve; teeth distinctly developed. In the 
brachial valve the cardinal area also bears an open delthyrium; the dental 
* Bulletin No. 8, American Museum of Natural History, p. 301, pi. xxiv, fig. 7. 1886. 
f Canadian Naturalist and Geologist, vol. iv, p. 349. 1859. 
