PLATE VII A. 



(Figare3l-12, 14-21,25, 28-31, 33-1^,4:1, 46, 48-53 by E. Emmons; 26, 27, 32 by J. M. Clarke; 45 by G. B. Simpson; 47 by R. P. 



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



Legeinl. D. Deltidium. s. Median septum, 



j. Cardinal process. s'. Latei^al septum. 



t. Teeth. s". Accessory lateral septum. 

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



fp. Crural plates. a'. Postei-ior adductor impressions. 

 c. Crura. 



Genus BILLINGSELLA, gen. nov. 



rape 230 



Orthis (Billingsella ??) Laurentina, Billing.s. 



Fig-. 1. View of the bi-achial 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 delthyiium ; the 

 outline of the muscular area and the median lidge. 



Fig. 4. The interior of the brachial valve, retaining the simiile cardinal process and the crural plates. 



Fig. 5. The central cai'dinal portion of both valves, enlarged 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 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 bi-achial valve ; showing the minute, linear cai-dinal process, and the small, 

 slightly divergent crural plates. X 3. 



Potsdam sandstone. Lake Pepin, Wisconsin. 

 Foi' further illustration of the species, see Report of the Geological Survey of Wisconsin, Volume 

 IV, plate i, tigui'es 4, 5. For illustration of Orthisina orientalAs, a congeneric form, see Bulle- 

 tin Am. Mus. Nat. Hist., Volume I, No. 5, p. 144, p)late 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. Thei-e 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. 



Pig. 12. The central portion of the intei-ior of a brachial valve, enlarged. Here, as in the preceding spe- 

 cies, thei'e is no ti-ace of a cardinal pi-ocess, though the quadruple division of the muscular 

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

 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. 



Page 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. 



