PLATE VII A— Continued- 
Fig. 17. A cardinal view of the same specimen. X 3. 
Fig. 18. An enlargement of the surface of an internal cast. The granules may be casts of punctse on the 
inner layer of the shell. X 6. 
Fig. 19. An enlargement of the external surface of the shell; showing the sharp concentric strise crossing 
the alternating plications. X 6. 
Fig. 20. The central cardinal portion of the brachial valve ; showing the broad, incurved delthyrium with 
a thickened area at its base, and the absence of a cardinal process. X (3. 
St. John group. St. John, N. B. 
Protorthis Quacoensis, Matthew. 
Fig. 21. The interior of a pedicle-valve. X 2. 
St. John group. Portland, N. B. 
For other illustration, see Trans. Royal Society of Canada, Sec. IV, 1885, plate v, figs. 20 a-o. 
Genus ORTIIIDIUM, gen. nov. 
Page 241. 
Orthidium gemmicula, Billings. 
Figs. 22, 23, 24. Three views of this shell. (After Billings.) 
Fig. 25. The interior of a brachial valve; showing the simple, erect cardinal process, coalesced with the 
crural plates. X 4. 
“ Point Ltvis ; in the upper part of the Limestone No. 2, Quebec group." (Billings.) 
Sub-genus POLYTCECHIA, sub-gen. nov. 
Page 239. 
Clitambonites (Polytcechia) apicalis, Whitfield: 
Fig. 26. The cardinal portion of the pedicle-valve. The deltidium has been removed exposing the con¬ 
cave spondylium (1) supported by a median septum (s) and lateral septa (s'). The accessory 
lateral ridges (s // ) are also seen. X 3. 
Fig. 27. The cardinal portion of the brachial valve ; showing in profile the lateral portions of the deltidium 
partially enclosing the simple cardinal process. The crural plates are very divergent and 
nearly parallel to the hinge-line. X 3. 
Figs. 28, 29, 30. Three views of the original specimen of the species, the last showing the high cardinal 
area and convex deltidium. X 3. 
Calcifei-ous beds. Fort Cassin, Vermont. 
For other illustration, see Bull. American Mus. Nat. Hist., Vol. I, plate xxiv, figs. 1-5. 
Genus SCENIDIUM, Hall. 
1 (See Plate VII, figs. 29-35. 
Page 2U. 
Orthis (Scenidium ??) Merope, Billings. 
Fig. 31. A view from the brachial valve ; showing the area and foramen of the opposite valve. X 4. 
Fig. 32. The interior of the brachial valve; showing the simple cardinal process and the crural plates. 
The deltidial cavity is thickened transversely, and from its center a low median ridge extends 
forward. X 4. 
Hudson River group. Cincinnati, Ohio. 
Scenidium Halli, S,afford. 
Fig. 33. The exterior of the pedicle-valve; showing the elevation of the beak. X 4. 
Fig. 34. A cardinal view of the same specimen ; showing the area and open delthyrium on both valves, 
with the slender process in the bottom of the brachial delthyrium. X 4. 
Fig. 35. The exterior of the brachial valve of the same specimen. X 4. 
Fig. 36. The interior of a brachial valve ; showing the triangular hinge-plate resting on the bottom of the 
valve, and the low median septum extending beyond the middle of the shell. 
The outline of the valve is more elongate than in the preceding specimen. X 4. 
Trenton limestone. (“ Glade Limestone ” of Safford.) Nashville, Tennessee. 
