PLATE IV E. 



Legend. V. Fonimen. jui. Anterior aililuctor scars, 



p. Pedicle-area, v jia. Pusterior atliliictor sears. 



g. External pedicle-groove. ' re. Reti'actor scars, 



j;'. The corresponding internal oleva- • t. Lateral scar.s. 



tion. ar. Anterior muscular ridges. 



DISCINI8CA, Dah,. 



I'.ige 120. 



Dl.-CINISCA LAMELLOSA, Bl()dori[). 



Fig. 1. The exterior of a pedicle-valve ; showing the broad, dcprcs.M^l 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 i'. 

 Recent. Peiii. 

 Fig. 3. The interior of a brachial valve ; showing the muscular iniiiressions. After Da viu.son. (Trans. 

 Linn. Soc, Ser. 2, Zool., vol. iv, pi. 2(), tig. 4. 1S88.) 



SCHIZOTRETA, Kutorga. 



Page l-.'O. 



OkBICULOIDKA (ScHIZOTKKTA) OVALIS. .-il). IIOV. 



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



groove. X B. . 

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

 Trenton limestone. Middleville, iV. T. 



ScHIZOTIiETA COMCA, Dwiullt. 

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

 of the anterior addnctor scars. X 2. From the oi-igijial specimen fignred by Dwiciirr (Amer. 

 Jonrn. Science, vol. xix, pi. xxi, tig. 11. 18S0). 

 Fig. 7. An impei'fect pedicle-valve; showing the great elevation of the apex and the short foramina! 

 groove. X 2. From the original specimen, op. cit., tig. ;J. 

 Trenton limestone. Newhargh, N. Y. 

 Fig. b. Outline profile of the conjoined valves. After Dwiuht. 



ORBICUI.OIDEA (ScHIZOTRETA ?) TENUn.AMEI.LATA, Hall. 

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



Niagara group. Western New York. 

 Fig. 10. The exterioi' of a pedi(de-valve. 

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



Niagara limestone. Handlton, Ontiirio. 



OEBICULOIDEA, UOrbignv. 



Page 1-20. 



Orbiciloioea la:mellosa, Hall. 

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



Trenton limestone. Middleinlle. N. Y. ■ 



Orbiculoiuea discus, Hall. 



Fig. \'.i. The interior of a pedicle-valve ; showing the elevatcil and much calloused walls of foiaininal 

 passage, and the opening at its postei'ior extremity. 



Lower Helderberg group. Near Glarksville, N. Y. 



OrBICULOIDEA NUMULUS. .sp. IIOV. 

 Fig. 14. The exterioi' of a pedicle-valve. 



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



Orbiculoiuea media. Hall. 



Fig. 1.1. A lirachial \-alve. 



Hamilton group. 8eneca county, N. Y. 

 Fig. 16. A pedicle-valve. 



Chemung group. Trmipsburg, N. Y. 

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

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



Hamilton group. Ontario cutmty, N. Y. 



