PLATE VII— Continued. 



Gexus IIKMIPIIONITES, Pani>ek. 



rage 538. 



Hemipkonitks, sp. ? 



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

 posite valve and the deltiilia of both valves are shown. X 2. 



Fiff. 21. A cardinal view of the same specimen ; showing' the iharacteristic contour upon which is liased 

 the separation of these forms from Clitambonitbs. X 2. 



Fig. 22. A specimen cut horizontally across the umbonal region of the pedicle-valve ; showing the united 

 dental lamelliE supported by a median septum. X 2. 

 Lower Silurian. Rnxsia. 



Genus CLITAMBONITES, Pander 



Page 233. 



Clitambonites adscendens, Paiidei-. 



Fig. 23. A cardinal view, giving' the sul)pyramidal contour characterizing this genus ; showing al.so the 



foramen in the deltidium. X 2. 

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

 Lower Silurian. Russia. 

 For further illustration, see Pander, Beitrage zur Geogn. russ. Reiches, ]>lates xvii, xviii, and de 

 Verneuil, Geologie de la Russia et des Mont, de I'Oural, plate xii, tig. 3. 



Clitambonite.s (Okthisina) anomala, Schlotheim. 



Fig. 25. A view of the pedicle-valve ; showing the great retrorsion of the apex, the high cardinal ai'ea of 

 the ])edicle-valve, and the perfoi'ated deltidium ; and also the area and <leltidium of the oppo- 

 site valve. (After de Verneuil, Geol. Russ. et des Mont, de I'Oural, plate xii, fig. 21. ) 



Fig. 26. The intei'ior of the bi'achial valve ; showing the extreme development of the cardinal area and 

 deltidium, the latter entirely obscuiing the cardinal process; the character of the muscular 

 and vascular .scars is also distinctly seen. (After Davidson.) 



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



For further illustration, see de Vernedil, Geol. Russ. et des Mont, de I'Oui'al, plate xii, fig. 2. 



Clitambonites plana, Ptiiuler. 



Fig. 28. The interior of the pedicle-valve ; showing the radiating ridges beneath the spondylium. (After 

 Davidson, Intiod. Foss. Brach., jilate viii, fig. 153.) 



Genus SCENIDIUM, Hall. 



(See Plate VIIa.) 

 Page 241. 



Scenidium pyramidale, Hall. 

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

 Pig. 29. View of the type-specimen ; showing the o])en delthyrium in each valve. X 2. 

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

 X 2. 



Niagara group. Lockport, N. Y. 



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 cardinal view of conjoined valves ; showing the concave plate in the delthyrium (d), the hinge- 

 plate (a) and the median septum (s). X 8. 



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



. septum. X 8. 

 Fig. 35. The interior of a pedicle-valve with an i>pen delthyrium. X 8. 

 Lowei- Helderberg grouj). Near Clarksville, N. Y. 



