PLATE IV e. 
Fig. 
Fig. 
Fig. 
Fig. 
Fig. 
Fig. 
Fig. 
Fig. 
Fig. 
Fig. 
Fig. 
Fig. 
Fig. 
Fig. 
Fig. 
Legend. F. Foramen. 
p. Pedicle-area, 
g. External pedicle-groove, 
g'. The corresponding internal eleva¬ 
tion. 
aa. 
pa. 
DISCINISCA, Dall. 
Anterior adductor scars. 
Posterior adductor scars. 
Retractor scars. 
Lateral scars. 
Anterior muscular ridges. 
Page 120. 
Discinisca lamellosa, Broderi[>. 
1. The exterior of a pedicle-valve; showing the broad, depressed pedicle-area, and the oval, direct 
perforation. 
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 f. 
Recent. Peru. 
3. The interior of a brachial valve; showing the muscular impressions. After Davidson. (Trans. 
Linn. Soc., Ser. 2, Zool., vol. iv, pi. 26, fig. 4. ' 1888.) 
SCHIZOTRETA, Kutorga. 
Page 120. 
Orbiculoidea (Schizotreta) ovalis, sp. 110V. 
4. A pedicle-valve from which the shell has been partially broken ; showing the short foraminal 
groove. X 3. 
5. Profile view of the same specimen ; showing the convexity of the conjoined valves. X 3. 
Trenton limestone. Middleville, N. Y. 
Schizotreta conica, Dwight. 
6. The interior of a brachial valve; showing its extreme shallowness and also indicating the position 
of the anterior adductor scars. X 2. From the original specimen figured by Dwight (Amer. 
Journ. Science, vol. xix, pi. xxi, fig. 11. 1880). 
7. An imperfect pedicle-valve; showing the great elevation of the apex and the short foraminal 
groove. X 2. From the original specimen, op. cit., fig. 3. 
Ti •enton limestone. Newburgh, N. Y. 
if. Outline profile of the conjoined valves. After Dwight. 
Orbiculoidea (Schizotreta?) tenuilamellata, Hall. 
9. The exterior of a brachial valve ; showing the elevated somewhat lamellose growth-lines. X 2. 
Niagara group. Western New York. 
10. The exterior of a pedicle-valve. 
11. Profile of the same. (This is the Piscina clam of Spencer, = I), solitaria, Ringueberg.) 
Niagara limestone. Hamilton, Ontario: 
ORBICULOIDEA, D’Orbigny. 
Page 120. 
Orbiculoidea lamellosa, Hall. 
12. Thejaxterior of a brachial valve. X 2. 
Trenton limestone. Middleville, N. Y. 
Orbiculoidea discus, Hall. 
13. The interior of a pedicle-valve ; showing the elevated and much calloused walls of foraminal 
passage, anil the opening at its posterior extremity. 
Lower Helderberg group. Near Clarksville, N. Y. 
Orbiculoidea numulus, sp. nov. 
14. The exterior of a pedicle-valve. 
Lower Helderberg group (Waterlime). Marshall, N. Y. 
Orbiculoidea media, Hall. 
15. A brachial valve. 
Hamilton group. Seneca county, N. Y. 
16. A pedicle-valve. 
Chemung group. Troupsburg, N. Y. 
17. The interior of a pedicle-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. 
