PLATE XV a. 
(Figures 1-18, 20-22, 24-28, 39, 40, 43 by E. EMMONS; 19. 23, 34, 35, 37, 38 by G. B. Simpson; 29, 30 by J. M. Clarke; 41, 42 
by C. E. Beecher; 31-33 copies.) 
Legend. 
D. 
C. 
ps. 
F. 
t. 
d. 
Deltidium (pedicle-valve). 
Deltidium (brachial valve). 
Pedicle-sheath. 
Foramen. 
Teeth. 
Dental lamellae. 
Spondylium. 
j. Cardinal process, 
c. Crura. 
br. Brachial ridges, 
a. Anterior adductor scars, 
a'. Posterior adductor scars, 
r. Diductor scars, 
x. Scar^of attachment. 
Genus CLITAMBONITES, Pander. 
(See Plate VII.) 
Fage 233. 
Clitambonites Verneuili. (von Eichwald) Billings (= Hemipronites Americanus, 
Whitfield). 
Figs. 1, 2. Opposite sides of conjoined valves. Figure 2 shows that the deltidium has been lost, exposing 
the spondylium. 
Fig. 3. The interior of a pedicle-valve which does not retain the deltidium ; showing the concave delthy- 
rial plate or spondylium supported by a median septum. 
Fig. 4. A view of the same specimen, looking into the umbonal cavity of the valve. 
Trenton horizon. Cannon Falls, Minnesota. 
Figs. 5, 6. Interiors of brachial valves; showing the simple cardinal process abutting against the deltidium, 
and the quadripartite impression of the adductor muscles. 
Trenton horizon. Island of Anticosti. 
Figs. 7, 8. Profile and cardinal views of a small pyramidal specimen which may be a variety of this spe¬ 
cies. • The deltidia of both valves are retained, that of the pedicle-valve being perforated by a 
large foramen. 
Trenton horizon. Cannon Falls, Minnesota. 
Genus HIPPARIONYX, Vanuxem. 
(See Plate IX.) 
Page 257. 
Hipparionyx proximus, Vanuxem. 
Fig. 9. The interior of a pedicle-valve drawn from a gutta-percha impression of a natural mould ; show¬ 
ing the character of the cardinal area and dental lamellae, the great size of diductor scars, the 
margins of which are thickened and elevated by the deposition of testaceous matter. The 
surface of the elevations thus formed is strongly pitted. The specimen also shows the low 
median septum dividing the adductor impression, which in the umbonal region unites with the 
dental lamellae to form an apical callosity. 
Fig. 10. The cardinal process and crural plates of the brachial valve. The crenulations of the margin of 
the valve are seen to extend almost to the base of the process. 
Oriskany sandstone. Albany county, N. Y. 
Fig. 11. Profile of an internal cast of the two valves. The specimen is drawn with the brachial valve above 
and shows the relative convexity of the valves and the extent of the crenulated margin toward 
the apices. 
Oriskany sandstone. Cayuga, Province of Ontario. 
For further illustration, see Palaeontology of New York, Volume III, plates 89, 90. 
Genus LEPTELLA, gen. nov. 
Page 293. 
Leptella sordida, Billings (sp.). 
Figs. 12, 13. Two views of a specimen retaining both valves, and showing the outline, contour and general 
external characters of the species. The delthyrium of the pedicle-valve is partially closed by 
a convex deltidium. X 3. 
Fig. 14. The interior of a pedicle-valve; showing the cardinal area, deltidium and teeth, but no trace of 
the muscular scars is retained. X 3. 
