PLATE XL. 



(Figures 1-3, 6, 7, 10, 12-21, 23-31 by E. EuMONS; 4, 5, 22 by R. P. Whitfield; 8, 9, U by G. B. Simpson.) 



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



hp. Hinge-plate. r. Diductor scars, 



vs. Median cleft of hinge-plate. a. Antei-ioi- adductors. 



OS. Crural plates. a'. Postei^ior adductors. 



8. Median septum. v. Vascular sinuses. 

 1. Loop. 



Genus WHITFIELDELLA, gen. nov. 



Page 68. 

 WHITHELDELLA INTERMEDIA, Hilll. 



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



lamella. X 2. 

 Fig. 2. Cardinal portion of the brachial valve ; showing the median division of the hinge-p]ate into two 



triangular processes. X 4. 



Clinton group. Hamilton, Ontario. 



WniTFIELDELLA NAVIFORMIS, Hall. 



Fig. 3. The cardinal portion 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. Wegtem New York. 



WHITFIELDELLA NITIDA, Hull. 



Fig. 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 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 lepre- 



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



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

 FigB. 8, 9. Two views of a large and transvei-se example ; the usual form occurring in this locality. 



Niagara group. Wa/dron, Indiana. 

 Fig. 10. An internal cast of conjoined valves ; showing the position of the dental plates [in the jiedicle- 



valve, the impression of the divided hinge-i)late, muscular seal's and vascular sinuses in the 



brachial valve. X 2. 



Niagai-a dolomites. Milwaukee, Wisconsin. 

 Fig. 1L[^ 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 prevailing foi-m of the species at 



this locality. X 2. 



Niagara group. Louisville, Kentucky. 



WHITFIELDELLA DIDYMA, Dallliail. 



Figs. 14, 15. Two views of an average specimen; showing the usual form of the shell, and the nai-row, 

 elevated umbo of the pedicle-valve. 



Wenlock limestone. Island of Gotland. 



