PLATE IV E. 



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



p. Pedicle-area. > pa. PostcM-ior adductor scars. 



g. External pedicle-groove. " re. Retractor scara. 



g'. The cori-esponding internal &^yar' " t. Lateral scars. 



tion. ar. Anterior muscular ridges. 



DISCINISCA, Dall. 



Papre liO. 

 Dl.'iCINlSCA LAMELLOSA, Brodcii|>. 



Fig. 1. The exterior of a pedicle-valve ; show-ing the bi-oad, depressed pedicle-area, and the oval, direct 

 perforation. 



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

 larged view is given on Plate IV f. 

 Recent. Pa-u. 



Fig. 8. The interior of a bi-achial valve ; .showing the muscular impression.s. AfUn- David.son. (Trans. 

 Linn. Soc, Ser. 2, Zoo!., vol. iv, pi. 26, tig. 4. 1888.) 



SCHIZOTRETA, Kutorga. 



Page 120, 



OrBICULOIDEA (ScIIIZOTKETA) OVALIS, .'^1). lUiV. 



Fig. 4. A pedicle-valve fi-om which the shell has been partially bi'oken ; showing the short foraminal 



groove. X 3. . : 



Fig. 5. Profile view of the same specimen ; showing the convexity of the conjoined valves. X 3. 

 Trenton limestone. Middleville, N. T. '[•' " 



SCHIZOTRETA CONICA, Dvvioht. 



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. Prom the original specimen figured by Dwight (Amer. 

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



Pig'. 7. An imperfect pedicle-valve ; showing the great elevation of the apex ami the short foraminal 

 groove. X 2. Fi-om the original specimen, op. cit., fig. H. 

 Trenton limestone. Newbtirgh, iV. Y. 



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



ORBICULOIDEA (ScHIZOTRETA ?) TEi\UILAMEI,LATA, HilU. 



Pig. . 9. The exterior of a brachial valve ; showing the elevated somewhat lamello.se growth-lines. X 2. 



Ni.agara group. Western iVeio York. 

 Pig. 10. The extei'ioi' of a pedicle-valve. 

 Fig. 11. Profile of the same. (This is the DUcina clara of Spencer, = D. .lolitaria, Ringueberg.) 



Niagara limestone. Haiii'ilton,, Oiitdrio. 



ORBICULOIDEA, D'Orbignv. 



Page 1-20. 

 OrBICULOIDEA LAJlELLOSA, Hull. 

 Fig. 12. The_exterior of a brachial valve. X 2. 



Trenton limestone. Middleville, N. Y.  



OrBICULOIDEA DISCUS, Hall. 

 Fig. 18. The interior of a pedicle-valve ; showing the elevated and much calloused walls of foranunal 

 passage, and the opening at its posterior extremity. 



Lower Helderbei-g group. Near Clarksville, N. Y. 



OrBICULOIDEA NUMULUS, Sj). IIOV. 

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



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



OrBICULOIDEA MEDIA, H.'lU. 

 Fig. 1.5. A brachial valve. 



Hamilt(ni group. Seneca county, N. Y. 

 Fig. 16. A pedicle-valve. 



Chemung grouj). Troiipshurc/, N. Y. 

 Fig. 17. The interior of a peilicle-valve. retaining the shell over the posterior segment only, but showing 

 the elevated pedicle-area and the perforation at its distal extremity. 

 Hamilton group. Ontario county, N. Y. 



