PLATE IV D. 



Legend, a. Deltidimn. m. Median scars. 



1>. Doltidial slope. n. Anterior scars, 



cc. Cardinal area. o. Lateral seal's. 



eg. Cardinal groove. p. Postmedian .-^cai-s. 



cr. Ci-escent. q. Crown of crescent. 



li. Aroal bordei-s. r. Side of crescent. 



i. tJmbonal chambei-s. u. Pallial sinuses or ndges(!). 



j. Platform. 



MONOMEKELLA, IJili.ixgs. 



Page 40. 



MONOMERKLT-A KiNGI, sp. UOV. 



Fig. 1. An internal cast of a pedicle-valve; showing the very short umbonal chambers and the shaiply 



defined mu.«cular iin)>ressions. 

 Fig. 2 The opposite side of the same specimen ; showing the internal characters of the brachial-valve. 

 Niagara limestone. Hawthorne, Illinois. 



MONOMERELLA, .Sp. ? 



Fig. ;!. The inner side of a specimen retaining the shell, believed to be a brachial valve of some species 

 of this genus. This specimen is considered by Whitb.wes as the pedicle-valve of Rhinoholuji 

 Galteiisis, Billings. Shoul<l Mr. Whitk.wes' opinion prove correct, it will probably be neces- 

 sary to remove Billings' species to some other genus. 



Fig. 4. The extei-ior of the same specimen. 



Guelph limestone. Oalt, Ontario. 



MOXOMERELLA GrEENII, -Sp. IIOV. 



Fig. "). An internal cast of a pedicle-valve ; showing the extremely small umbonal chambers ami the 

 sharply ilefined crescent, cardinal groove and lateral scars. 

 Niagara limestone. Grafton, WUconsiii. 



Fig. G. An interior ca.«t of the brachial valve ; showing a portion of the broad area of contact, the plat- 

 form scars, with the <livei'ging anterior ridges. 

 Niagara limestone. Rising Sun, Ohio. 



Fig. 7. The interior of a brachial valve, from a gutta-pei'cha cast of a natural ijupression. The crescentic 

 fidcrnni is ex<^eedingly strong and the platform very obscure. 



Fig. S. An internal cast of a pedicle-valve ; showing the very broad cardinal margin and its lateral exten- 

 sion ; also the faint umbonal cavities and the conspicuous cardinal groove and crescent. 



Fig. 9. The intei-ioi- of a bi'achial valve, with sharply defined terminal scars and anterior ridges. From 

 a gutta-percha cast. 



Fig. iO. .\n internal cast of a brachial valve ; showing, in the matrix, the impression of the cardinal area. 

 The platform scai-s are accompanied by scarcely any thickening of the shell. 

 Niagara limestone. Grafton, Wi.ieonsiii. 



^lONOMERELLA OVATA, ViU'. LATA, WllitcaveS. 



Fig. 11. The exterior of a pe<licle-valve. From the original specimen figured by Whitbaves (Paleozoic 

 Fos-sils, vol. iii, jit. 1, pi. 2, fig. 2a). 



Fig. 12. A portion of the interior of a pedicle-valve. From Whiteaves' original {op. cit-, pi. 8, fig. 2). 



Guelph limestone. Durham, Ontario. 



MONOMERELLA OVATA, WllitcaveS. 



Fig. 13. View from the brachial side of a fine specimen retaining the valves in conjunction. 



Fig. 14. Profile of the same. From White.\ve,s' original specimen (op. cit., pi. 8, tigs. 1, la). 



Fig. 1."). The iTiterioi- of a pedicle-valve ; showing the broad cardinal ai-ea and deltidial slope, the shallow 

 imilMiniil chambers, the deep cardinal groove and lateral scars of the crescent, and the slii;li'ly 

 elevated anterior edge of the platform. From White.wes' original specimen (o/j. cit. \\ •». 

 fig. 16). 



Guelph limestone. Durham, Ontario. 



i 



