95 
Dimensions. —Type specimen : length, 5'16 mm. ; width, 8'3 mm. 
Relationships. —The coarse plications in this shell resemble to some extent 
those of B. major , Walcott, 1 from the Upper Cambrian of Wisconsin. Our 
species differs not only in the fewer folds but in the be called shoulders and 
deeply depressed median area. 
Genus Eoorthis, Walcott. 
Eoorthis flexilis, sp. nov. Plate VI., figs. 10-11. 
Description. —'Pedicle valve depressed convex, incurved at the margins, 
subcircular in outline, with straight cardinal line and.acutely produced 
extremities. Anterior margin somewhat truncate, sides obliquely rounded. 
Surface relieved by about 17 radiating folds, inclined to be flexuose and 
with a few secondary ribs interspaced between the main folds. No. 7910 is a 
natural cast of the pedicle valve, and 7911 is'copied from a wax squeeze of the 
mould of the same valve. 
Dimensions. —Length, 3'33 mm. ; width, 7'16 mm. 
Relationships. —-Probably the nearest allied form is Eoorthis merope 
Billings sp. 2 , from the lowest beds of the Trenton Limestone. It differs 
from our species in the greater number of riblets, but agrees perfectly in 
outline. 
E. flexilis is also closely related to Eoorthis carausii , Salter sp. 3 , of the 
Lower Arenig of Wales, but the width of the latter shell is much less in 
proportion to height. 
Eoorthis concinna, Chapman sp. 
Chonetes concinna, Chapman, 1904, Pec. Geol. Surv. Viet., vol. I., pt. 3, 
p. 223, pi. XXL fig. 3. 
Observations .—This fossil was formerly referred to Chonetes , partly on 
account of the negative cavity of the cardinal line being bridged across by 
mineral replacements which may originally have been based on a striated 
condition of the shell in that area. A similar denticulate structure is seen 
in Eoorthis kayseri, Walcott sp. 4 . The form of the value is subquadrate, 
with a straight hinge — line and strong median sulcus on the ventral surface y 
(not dorsal as stated in original description). r lhe shell was probably of 
thin texture and finely and numerously striated. 
E. concinna generally resembles certain species of the genus found in 
Middle and Upper Cambrian beds in North America and China, though 
none appears to be closely related excepting perhaps E . linnarssoni, Kayser 
sp. 5 , from the Upper Cambrian of Shan-tung, which differs in the coarser 
costation and more evenly rounded outline of the valve. The above species 
also appears to be related to E. flexilis of the Heathcote series, but the 
valves are longer and the ornament finer. 
Eoorthis vespertilioides, Chapman sp. 
Orthis ( Hebertella ) vespertilioides , Chapman, 1904, Bee. Geol. Surv. 
Viet., vol. I., pt. 3, p. 224, pi. XXI., fig. 6. 
Observations. —A ventral valve, having a strong median sinus and 
inflated lateral areas. It is of the general type of Eoorthis kichouensis, 
Walcott sp. 6 , of the middle Cambrian of Shan-si, China ; but the 
Heathcotian species is more laterally elongate and with acute cardinal 
angles. 
1 Smithsonian Misc. Colls., vol. LIII., No. 1810,1908, p. 101, pi. X., figs. 1, la. 
* Orthis merope, Billings. Geol. Surv. Canada, Pal. Fossils, vol. I., 1865, p. 139, fig. 116 a-c. 
* Orthis carausii, Salter, Davidson. Geol. Mag., 1868, p. 315, pi. XVI., fig. 23. 
4 Research in China, vol. III.. 1913, pi IV., fig. 8b. 
5 Orthis linnarssoni, Kayser, in Richthofen’s “China,” vol. IV., 1883, p. 31, pi. III., fig 1. Eoorthis 
linnarssoni, Kayser sp, W alcott, Research in China, vol. III., 1913, p. 83, pi. IV., figs. 11, 11a. 
6 Research in China, vol. III., 1913, p, 8?, pi IV., fig. 10. 
