PLATE XL. 



(Figures 1-3, c, 7, i", li-i\, 'iS-Sl by E. Emmoks; 4, 5, 2i by K. P. Wuiti'IEi,!); S, 8, II by G. B. Simpson.) 



Legend : dl. Dental lamellie. x. Stem of loop. 



hp. Hinyi»-plate. i-. Diductoi- scars, 



vs. Median cleft of hinge-plate. a. Anterior adductors, 



cs. Urural i>lates. a'. Posterior ailductoi's. 



8. Me<iian septum. v. Vascular siniisea. 



1. Loop. 



Genus WHITFIELDELLA, gen. nov. 



I'ase 58. 

 WlIITflELDELLA INTEKMEDIA, Hull. 



Fig. 1. Tlie interioi- of a pedicle-valve ; showing the unclosed delthyrium, teeth and convergent dental 



lamellae. X 2. 

 Fig. 2. Cardinal portion of the hrachial valve j showing the median division of tlie hinge-jilate into two 



ti'iangular processes. X 4. 



Clinton group. Hamiltim, Ontario. 



WniTFIELDELLA NAVIFORMIS, Hall. 



Fig. 3. The cardinal portion of a brachial valve ; showing the structure of the hinge-plate, \vliii:h is prima- 

 rily divided medially, the median cleft being partially filled by an erect lobe. X H. 

 Clinton gi-oup. Western Neio York. 



Whitfieldella nitida, Hall. 



I'^ig. 4. The cardinal portion of a pedicle-valve ; showing the teeth, and the foramen 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 sejitum 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 l)oth of these figures the horizontal stem of the loop as repre- 

 sented is much loo long, and in figure 7, the doited line from the letter x should terminate at 

 this stem and not on ttie supporting matrix, (c.) 



Figs. 8, fl. Two views of a large and transverse examiile ; the usual form occurring in this locality. 

 Niagara group. Waldron, Indiana. 



Fig. 10. An internal cast of conjoined valves ; showing the positicm 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. 



Niagai'a dolomites. MilwauJcee, \Vi.sconsin. 



Fig. 11. ^Dorsal view of an elongate shell, having the greatest width anteriorly. 

 Niagara group. Waldron, Indiana. 



Figs. 12, 13. Dorsal and antericu- marginal views of a .shell ; showing the prevailing foi-m of the species at 

 this locality. X 2. 



Niagara group. LuuisviUe, Ke?itucky. 



Whitfieldella didyma, Dalinan. 



Figs. 14, 15. Two views of an avei'age specimen ; .showing the usual form of the shell, and the narrow, 

 elevated umbo of the pedicle-valve. 



Wenlock limestone. Island of Gotland. 



