PLATE VII A. 



(Figures 1-12, 14-21, 25, 28-31, 33-C2, 4t, 46, 48-s;ibv E. Emmons; 2(i, 27, 32 by J. Jr. Clarke; 46 by G. B. Simpson; 47 by 11. 1'. 



WiliTFiEi.D; l.i, 22-24, 43 copies.) 



Legenil. D. Deltidium. s. Median septum, 



j. Cardinal jiroeess. s'. Latei'al scptnni. 



t. Teeth. s". A(:ce.«soi-y lateral septum. 



1. Spondylium. a. Anterior adductcir impressions, 



fp. Ci-ural plates. a'. Poatericpr adductoi- impressions. 



c. Crura. 



Genus BILLINGSELLA, gen. nov. 



rape 230 



Orthis (BiLLiNosELLA ??) Laurentina, Billing.^. 



Fig. 1. View of the brachial valve ; showing the simple plications, area and deltidiiuu of the ojiposite 

 valve. 



Fig. 2. Profile of the same specimen. 



Fig. S. The interior of the pedicle-valve ; showing the cardinal area, teeth and covered ihdtliyrium ; the 

 outline of the muscular area and the median ridge. 



Fig. 4. The interior of the Ijrachial valve, retaining the simple cardinal process and the crural plates. 



Fig. ^. The central cardinal portion of both valves, enlai'ged to show the character of the deltidia. On 

 the brachial valve the deltidium is incomplete, the latei'al portions not having united, and thus 

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



Fig. 6. The same parts in another specimen in which the deltidium of the brachial valve is neai-ly com- 

 plete. X 3. 



Anticosti gi-oup. Anticosti. 



Billingsella Pepina, Hill!. 



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 furtheiMllustration of the species, see Repoi-t of the Geological Survey of Wisconsin, Volume 



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



tin Am. Mus. Nat. Hist., Volume I, No. 5, p. 144, plate xiv, tig. G. 



Orthis (??) Mycale, Billiiig.s. 



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. Thei'e is no evidence of a cardinal process in the delthyrium. X 2. 



"Paint 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 rausculai- 

 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 PKOTORTHIS, gexV. nov. 



rage 231 



I'uoTORTiiis Billingsi, ntirtt. 

 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 spondylinm which closes the 

 delthyrium below. X 3. 



