PLATE VII A. 



(Figures 1-12, H-2I,'25, 28-31,33-1.!, 11, 46, 48-53 by E. Emmons; 2C, 27. 32 by J. M. Ci.auke; 45 by G. B. Simpson; 47 bv R. P. 



Whitfield; 13, 22-24. 43 copies.) 



Legend. D. Deltidium. s. Meiiian septum. 



j. Caiilinal process. s'. Lateral septum, 



t. Teeth. s". Accessory lateral septum. 

 1. Spoiulylium. a. Anterior adductor impi-essions. 



fji. Crural plates. a'. Posteiior adductor impressions. 

 c. Crura. 



Genus BILLTNGSELLA, oex. .nov. 



rage >,iO 



Okthis (BiLLiNG.sELLA ??) Laurentina. Billing.-*. 



Fig. 1. View of the lu-achial valve ; showing the simple plications, area and deltidium of the opposite 

 valve. 



Fig. 2. Profile of the same specimen. 



Fig. 'A. The interior of the pedicle-valve ; showing the cai-dinal area, teeth and covered delthyrium ; the 

 outline of the mu.?cular area and the median ridge. 



Fig. 4. The interior of the bi'achial valve, retaining the simple I'ardinal 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 [lorlions not having united, and thus 

 exposing the postexior edge of the cardinal process. X 3. 



Fig. 6. The .same jiarts in another specimen in which the deltidium of the brachial valve is nearlv com- 

 plete. X 3. 



Anticosti group. Anticostl. 



BlLUNtiSELLA PePIiNA, HuU. 

 Fig. 7. An internal cast of the jiedicle-valve. X 3. 

 Fig. 8. The interioi' of the same valve, from a gutta-percha iiniiression of a natural mould ; showing the 



broad cardinal area, the convex deltidium, teeth, outline of the musculai- area and a single paii- 



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, Wiscotisin. 

 For furtheiMllusti-ation of the species, see Report of the Geological Survey of Wisconsin, Volume 

 IV, plate i, figures 4, 5. For illustration of OrthUina orientalis, a congeneric form, see Bidle- 

 tin Am. Mus. Nat. Hist., Volume I, No. 5, p. 144. jilate xiv, fig. 6. 



Orthis (??) Mycale, Billings. 



Fig. 10. The exterior of a brachial valve, tVora the original specimen. 



Fig. 11. The interior of the same specimen, enlarged; .showing the quadripartite muscular imjirint .and 

 the crural plates. Theie is no evidence of a cai-dinal process in the delthyrium. X 2. 



"Point Levis; in the uijper part of Limestone No. 2, Quebec group." (Billings.) 



Orthis (??) Tritonia, Billings. 



Fig. 12. The central poi-tion of the interior of a bi-achial valve, eidarged. Here, as in the preceding spe- 

 cies, there is no trace of a caniinal pi'oce.ss, though the quadruple division of the muscular 

 imprint indicates that this is the brachial and not the pedicle-valve. From one of the oi-iginal 

 specimens. X 3. 



Fig. 13. The exterior of the brachial valve. (After Billinus.) 



" Point Lici.s ; in the upper part of Lime.itone No. 2, Quebec group." (B\\,usqs.) 



GexNus PKOTORTIIIS, gen. nov. 



I';i^'e231 



Pkotortiii.'* BiLLiNosi, Haitt. 

 Fig. 14. The exterior of a pedicle-valve. X 2. 

 Fig. 15. The interioi' of a bracliial valve. X 2. 



Fig. 16. The exterior of a small pedicle-\"a!ve ; showing the concave plate or spondy Hum which closes the 

 delthyrium below. X 3. 



