PLATE VII a. 
(Figures 1-12,14-21,25, 28-31,33-12,11,46,48-53 by E. Emmons; 26, 27, 32 byJ. M. Clarke; 45 by G. B. Simpson; 47 by It. 1’. 
Whitfield; 13, 22-21, 13 copies.) 
Legend. D. Deltidium. 
j. Cardinal process, 
t. Teeth. 
1. Spondylium. 
fp. Crural plates, 
c. Crura. 
s. Median septum, 
s'. Lateral septum. 
s // . Accessory lateral septum, 
a. Anterior adductor impressions. 
a 7 . Posterior adductor impressions. 
Genus BILLINGSELLA, gen. nov. 
l’age 230 
Orthis (Billingsella??) Laurentina, Billings. 
Fig. 1. View of the brachial valve ; showing the simple plications, area and deltidium of the opposite 
valve. 
Fig. 2. Profile of the same specimen. 
Fig. 3. The interior of the pedicle-valve ; showing the cardinal area, teeth and covered delthyrium ; the 
outline of the muscular area and the median ridge. 
Fig. 4. The interior of the brachial valve, retaining the simple cardinal process and the crural plates. 
Fig. 5. The central cardinal portion of both valves, enlarged to show the character of the deltidia. On 
the brachial valve the deltidium is incomplete, the lateral portions not having united, and thus 
exposing the posterior edge of the cardinal process. X 3. 
Fig. 6. The same parts in another specimen in which the deltidium of the brachial valve is nearly com¬ 
plete. X 3. 
Anticosti group. Anticosti. 
Billingsella Pepina, Hall. 
Fig. 7. An internal cast of the pedicle-valve. X 3. 
Fig. 8. The interior of the same valve, from a gutta-percha impression of a natural mould ; showing the 
broad cardinal area, the convex deltidium, teeth, outline of the muscular area and a single pair 
of vascular trunks. X 3. 
Fig. 9. The interior of a brachial valve; showing the minute, linear cardinal process, and the small, 
slightly divergent crural plates. X 3. 
Potsdam sandstone. Lake Pepin, Wisconsin. 
For further illustration of the species, see Report of the Geological Survey of Wisconsin, Volume 
IV, plate i, figures 4, 5. For illustration of Orthisina orientalis, a congeneric form, see Bulle¬ 
tin Am. Mus. Nat. Hist., Volume I, No. 5, p. 144, plate xiv, fig. 6. 
Orthis (??) Mycale, Billings. 
Fig. 10. The exterior of a brachial valve, from the original specimen. 
Fig. 11. The interior of the same specimen, enlarged; showing the quadripartite muscular imprint and 
the crural plates. There is no evidence of a cardinal process in the delthyrium. X 2. 
“ Point Levis ; in the upper part of Limestone No. 2, Quebec group.” (Billings.) 
Orthis (??) Tritonia, Billings. 
Fig. 12. The central portion of the interior of a brachial valve, enlarged. Here, as in the preceding spe¬ 
cies, there is no trace of a cardinal process, though the quadruple division of the muscular 
imprint indicates that this is the brachial and not the pedicle-valve. From one of the original 
specimens. X 3. 
Fig. 13. The exterior of the brachial valve. (After Billings.) 
“ Point Levis; in the upper part of Limestone No. 2, Quebec group.” (Billings.) 
Genus PROTORTHIS, gen. nov. 
l’age 231 
Protorthis Billingsi, Hai-tt. 
Fig. 14. The exterior of a pedicle-valve. X 2. 
Fig. 15. The interior of a brachial valve. X 2. 
Fig. 16. The exterior of a small pedicle-valve ; .showing the concave plate or spondylium which closes the 
delthyrium below. X 3. 
