PLATE VII— Continued. 



Genus HEMIPRONITES, Pandee. 



Page 23S. 



Hemipronites, sp. ? 



Fig. 20. A view of the pedicle-valve, the cardinal area beirifr in the plane of vision. The area of the op- 



jiosite valve and the deltidia of both valves are shown. X 2. 

 Fig-. 21. A cardinal view of the same specimen ; showing the iharactenstic contour upon which is based 



the seij.-iralion of these forms from Clitambonitbs. X 2. 

 Fig. 22. A specimen cut horizontally acro.ss the nmbonal region of the i^edicle-valve ; showing the united 



dental lamellaj supported by a median septum. X 2. 

 Lower Siluiian. JRunsia. 



Genus CLITAMBONITES, Pander. 



Page 233. 



Clitambonites adscendens, Piiiider. 



Fig. 23. A cardinal view, giving the subpyramidal contour characteiizing this genus; showing also the 



foi-amen in the deltidium. X 2. 

 Fig. 24. A pedicle-valve with the apex cut away; showing the peculiar internal structure of this valve. X 2. 

 Lower Silui-ian. liussia. 

 For fni'ther illustration, see Pander, Beitrase zur Gengn. I'uss. Reiches, jilates xvii, xviii, and db 

 Vernbuil, Geologie de la Russie et des Mont, de I'Oural, plate xii, tig. 3. 



Clitambonites (Orthisina) anomala, Schlolheim. 



Fig. 25. A view of the pedicle-valve ; showing the great i-etrorsion of the apex, the high cardinal area of 

 the jiedicle-valve, and the perfin-ated deltidium ; and aviso the area and deltidium of the oppo- 

 site valve. (Aftei- dk Verneuil, Geol. Russ. et des Mont, de I'Oural, plate xii, fig. 26.) 



Fig. 26. The interioi- of the brachial valve ; showing the extreme development of the cardinal area and 

 deltidium, the latter entii'ely obscuiing the cardinal pi'ocess ; the character of the muscular 

 and vascular scars is also distinctly seen. (After David.son.) 



Fig. 27. The interior of a pedicle- valve. (After Da vrBsoN.) 



For further illusti-alion, see de Vii:RNEDiL, Geol. Russ. et des Mont, de I'Oural, jjlate xii, fig. 2. 



Clitambonites plana, Paiidei-. 



Fig. 28. The interior of the pedicle-vah-e : showing the radiating ridges beneath the spondylium. (After 

 Davidson, Litrod. Foss. Brach., plate viii, tig. 153.) 



Genus SCENIDIUM, Hall. 



(See Plate VIIa.) 

 Page 241. 



SCENIIHUM pyramidale, Hall. 



(See Plate VIIa, figs. 29, 30.) 



Fig. 29. View of the type-specimen ; showing the ispen delthyriiun in each valve. X 2. 



Fig. 30. A cardinal view; showing- the size of the areas of the two valves and character of the delthyiium. 

 i.i il'litr.vi' X 2. 



Niagara group. Lockpm-t, N. T. 



SCENIDIUM INSIGNE, Hall. 



Fig. 31. A view of the brachial valve ; showing the concave plate (d) in the delthyrium of the pedicle- 

 valve. X 8. 



Fig. 32. The opposite side of the same specimen, pedicle-valve. X 8. 



Fig. 33. A cai-dinal view of conjoined valves ; showing the concave plate in the delthyrium (d), the hinge- 

 plate (a) and the median septum (s). X S. 



Fig. 34. The intei-ior of the brachial valve ; showing the elevated hinge-plate and the prominent median 

 sei;)tum. X 8. 



Fig. 35. The interior of a pedicle-valve with an open delthyi'ium. X 8. 

 Lower Helderberg group. Near Clarksville, N. Y. 



