PLATE IV E. 



Legend. F. Foramen. aa. Anterior adductor scars, 



p. Pedicle-area. pa. Posterior adductor scars, 



g. External pedicle-groove. ■ re. Retractor scars, 



g'. The corresponding internal eleva- t. Latei-al scars. 



tion. ar. Anterioi' muscular lidges. 



DISCINISCA, Dall. 



Page 120. 



Dl-^cinisca lamellosa, Brodeiip. 

 Fig. 1. The exterior of a pedicle-valve; showing the broad, depressed pedicle-area, and the oval, direct 



perforation. 

 Fig. 2. The interior of the same specimen ; showing the characters of the pedicle-area, of which an en- 

 larged view is given on Plate IV p. 

 Recent. Peru. 

 Fig. 3. The interior of a brachial valve ; showing the muscular impressions. After Davidson. (Trans. 

 Linn. Soc, Sei'. 2, Zool., vol. iv, pi. 26, Kg. 4. 188S.) 



SCHIZOTRETA, Kutoega. 



Page 120. 



Orbiculoidea (Schizotreta) ovalis, sp. uov. 



Fig. 4. A pedicle-valve from which the shell has been partially broken ; showing the short foraminal 



groove. X 3. 

 Fig. 5. Profile view of the same specimen ; showing the conve.\ity of the conjoined valves. X 3. 

 Trenton limestone. Middleville, N. Y. 



Schizotreta conica, Dwight. 



Fig. 6. The interior of a brachial valve ; showing its extreme shallowness and also indicating the position 

 of the antei-ior adductor scars. X 2. From the original specimen figured by Dwight (Amer. 

 Journ. Science, vol. xix, pi. xxi, fig. 11. 1880). 



Fig. 7. An imperfect pedicle-valve ; showing the great elevation of the apex and the short foraminal 

 groove. X 2. From the oi-iginal specimen, op. cit., fig. 3. 

 Trenton limestone. Newburgh, N. Y. 



Fig. 8. Outline profile of the conjoined valves. After Dwight. 



Orbiculoidea (Schizotreta?) tenuilamellata, Hall. 



Fig. 9. The exterior of a brachial valve ; showing the elevated somewhat lamellose growth-lines. X 2. 



Niagara group. Western Neio York. 

 Fig. 10. The exterior of a pedicle-valve. 

 Fig. 11. Profile of the same. (This is the Diseiim clara of Spencee, = D. solitana, Ringueberg.) 



Niagai-a limestone. ' Haiiiilton, Ontario. 



ORBICULOIDEA, D'Orbigny. 



Page 120. 



Orbiculoidea lamellosa, Htill. 



Fig. 12. The^exterior of a bi-achial valve. X 2. 



Trenton limestone. Middleville, N. Y. 



Orbiculoidea discus, Hall. 



Fig. 13. The interior of a pedicle-valve ; showing the elevated and much calloused walls of foraminal 

 passage, and the opening at its posterior extremity. 



Lower Helderberg group. Near Clarksville, N. Y. 



Orbiculoidea numulus, sp. iiov. 



valve. 



berg group (Waterlime). Marshall, 



Orbiculoidea media. Hall. 



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



Lower Helderberg group (Waterlime). Marshall, N. Y. 



Fig. 15. A brachial valve. 



Hamilton group. Seneca cowiity, N. Y. 

 Fig. It). A pedicle-valve. 



Chemung group. Tronpsburg, N. Y. 

 Fig. 17. The interior of a pedicle-vah-e, retaining the shell over the posterior segment only, liut showing 

 the elevated pedicle-area and the perfoi-ation at its distal extremity. 



Hamilton group. Ontario county, N. Y. 



