PLATE VIII. 



(Figures 1-18, 22-31 by R, P. WHITFIELD; 20, 21 by F. J. SwiNTON; 19 by G. B. SIMPSON.) 



Legend. D. Deltidium, pedicle-valve. b. Dental sockets. 



C. Deltidiiim, brachial valve. t. Teeth. 



^. Delthyrium. j. Cardinal process. 



F. Foramen. ' a. Adductor scars. 



F'. Groove on delthyrium, l>rachial valve. r. Anteiior diductor scars. 



A. Cardinal area : r' . Posteiior diductor scars, 

 a. Inner portion, 

 a'. Outer portion. 



Genus RAFUSfESQUINA, gkn. nov. 



(See Plate VIII, 6gs. 1-11 ; Plate IXa, tigs. 1, 2, 4 ; and Plate XVa, tigs. 37-39.) ' 



Page 281. 



Rafinesquina incrassata, Siiiford* (not Hall). 



Fig. 1. A view of the brachial valve of a large individual ; .showing the area and oi^en delthyrium of the 



pedicle-valve. 

 Fig. 2. The interior of the brachial valve ; showing the structure of the articulating apparatus and the 



musculai' impressions. 

 Fig. 3. A posterior view of the same specimen ; showing the bifui-cate, incisor-shaped cardinal process, 



its surface sloping biickward to the hinge-line, and partially covered by the deltidium. X 3. 

 Fig. 4. A cai'dinal view of a portion of the hinge and area ; showing the deltidia of both valves, that of 



the pedicle-valve having its surface distinctly gi-ooved. X 3. 

 Fig. 5. The internal cast of a pedicle-valve ; showing the great size of the diductor scai-s, and the filling 



of the foramen. 



Trenton horizon. Plattmnlle, Wisconsin. 



Rafinesquina alteknata, Connnl. 



Figs. 6, 7. Two views of a specimen presenting normal external characters. 



Fig. 8. An enlargement of a portion of the hinge-area; showing the deltidia of both valves, and the re- 

 tention of the foi-amen at maturity. X 3. 



Fig 9. The interior of a bi-achial valve ; showing the structure of the cardinal pi'ocess and the adductor 

 scars. 



Fig. 10. The interior of a pedicle-valve : showing the fiabellate diductor and the narrow adductor scars. 



Fig. 11. A posterioi- view of the articulating apparatus of the brachial valve. The incisoi'-shaped branches 

 of the cardinal process are widely divergent, and at the bottom of the bifurcation lies a narrow 

 callosity. The deltidium is well developed but not grooved in the middle, and the dental 

 sockets are deeply marked. X 3. 



Hudson River group. Cincinnati, Ohio. 

 For othei' illustrations, see Palasontologj- of Ohio, Vol. I, plate \\i, figs. 1-3 ; and Palaeontology of 

 New York, Vol. I, plates xxxi and xxxi A. 



Genus LEPTiENA, Dalman. 



Page 27B. 



LEPTiENA TENuiSTRiATA Soweiby (= L. vhomboidolis, Wilckeiis). 

 Fig. 12. The interior of a brachial valve. 

 Figs. 13, 14. Views of opposite sides of an individual in which the foi-amen is retained. 



Hudson River group. Oxford, Ohio. 

 Fig. 15. A portion of the hinge of a matui-e individual, enlarged ; showing the foramen situated in front of 

 the area, the slight development of the deltidium of the pedicle-valve, and Ihe gi-eat size of 

 that of the brachial \-alve, the latter being deeply grooved. X 3. 

 Hudson River group. Lebanon, Ohio. 

 Fig. 16. An enlarged cardinal view of the central portion of the brachial valve ; showing the deep groove 

 or central depression, the callosity conforming to the contour of the cardinal apophyses. 

 Hudson River gi-oup. Oxford, Ohio. 



* Since the true generic relations of the Chazy species, according to the present arrangement, is not fully ascertained, 

 this specitlc name is retained for the Trenton species. Should the original Leptana incrassata, of the Chazy, prove to be a 

 Eafinesquina, the Trenton form will retain the name of S. Minnen-Sensis, N. H. Winchell. 



