PLATE XL. 
(Figures 1-3, 6, 7, iO, 1-2-21, 23-31 by E. Emmons; 4, 5, 22 by R. P. Whitfield; S, 9, 11 by G. B. Simpson.) 
Legend : dl. Dental lamellae, 
hp. Hinge-plate, 
vs. Median cleft of hinge-plate, 
cs. Crural plates, 
s. Median septum. 
1. Loop. 
X. Stem of loop. 
1 -. Diductor scars, 
a. Anterior adductors, 
a'. Posterior adductors. 
V. Vascular sinuses. 
Genus WHITFIELDELLA, gen. nov. 
Pa.ge 58. 
White lELDELLA intermedia, Hall. 
Fig. 1. The interior of a pedicle-valve ; showing the unclosed delthyrium, teeth and convergent dental 
lamellae. X 2. 
Fig. 2. Cardinal portion of the brachial valve ; showing- the median division of the hinge-plate into two 
triangular processes. X 4. 
Clinton group. Hamilton, Ontario. 
Wiiitfieldella naviformis, Hall. 
Fig. 3. The cardinal jiortion of a brachial valve ; showing the structure of the hinge-plate, which is prima¬ 
rily divided medially, the median cleft being partially filled by an erect lobe. X 3. 
Clinton group. Western New York. 
Wiiitfieldella nitida, Hall. 
Fig. 4. The cardinal portion of a pedicle-valve; showing the teeth, and the foi-amen almost enclosed by 
the substance of the shell. X 3. 
Fig. 5. The cardinal portion of a brachial valve; showing the medially divided hinge-plate, the faint 
median septum and the elongate dental sockets. X 3. 
Fig. 6. A preparation of the spirals and loop in a specimen in which the entire brachidium has been 
detached from the crura and revolved through an arc of 180°, entirely reversing its normal 
position. 
Fig. 7. A profile of the same specimen. In both of these figures the horizontal stem of the loop as repre¬ 
sented is much too long, and in fig-ure 7, the dotted line from the letter x should terminate at 
this stem and not on the supporting mati-ix. (c.) 
Figs. 8, 9. Two views of a large and ti-ansverse example ; the usual form occurring in this locality. 
Niagara group. Waldron, Indiana. 
Fig. 10. An internal cast of conjoined valves; showing the position of the dental plates -in the pedicle- 
valve, the impression of the divided hinge-plate, muscular scars and vascular sinuses in the 
brachial valve. X 2. 
Niagara dolomites. Milwaukee, Wisconsin. 
Fig. IL^Dorsal view of an elongate shell, having the greatest width anteriorly. 
Niagara group. Waldron, Indiana. 
Figs. 12, 13. Dorsal and anterior marginal views of a shell; showing the pi-evailing foi-m of the species at 
this locality. X 2. 
Niagara group. Louisville, Kentucky. 
Wiiitfieldella didyma, Dalman. 
Figs. 14, 15. Two views of an average specimen; showing the usual form of the shell, and the narrow, 
elevated umbo of the pedicle-valve. 
Wenlock limestone. Island of Gotland. 
