PLATE IV D. 



Legend. a. Delticiiuin. 



b. Delti<lial slope. 



cc. Cardinal area. 



eg-. Cardinal groove. 



cr. Crescent. 



d. Areal borders. 



i. Umbonal chambers. 



j. Platform. 



Fig. 



Fig. 



Fig. 



Fig. 



Fig. 



Fig. 



Fig. 

 Fig. 

 Fig. 

 Fig. 



Fig 



Fit; 



ni. Median scars, 



n. Antei'ior scars, 



o. Lateral scars, 



p. Postmedian scars, 



q. Crown of crescent, 



r. Side of cres(tent. 



M. Pallial sinuses or ri 



ige.«(!). 



MONOMERELLA, Billings. 



Page 40. 



MONOMERKLT.A KiNGI, Sp. UOV. 



1. An internal cast of a pedic'.e-valve ; showing the \ery short umbonal chambers and the sharply 



defined inuscnlar impressions. 

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

 Niagara limestone. HawtJiorne, Illinois. 



MONOMERELLA, .sp. ? 



;!. 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 Whitkaves as the pedicle-valve of Rhinoholiut 

 Galtensis, Billings. Should Mi'. Whiteaves' opinion prove correct, it will probably he neces- 

 sary to remoN'e Billings' species to some other genus. 



4. The exterior of the same specimen. 



Guelph limestone. Gait, Ontario. 



MONOMERELLA GrEENH, sp. IIOV. 



0. An internal cast of a pediole-valve ; showing the extremely small umbonal chambers and the 

 sharply defined crescent, cai-dinal groove and lateral scars. 

 Niagara limestone. Orafton, Wisconsin. 



0. An interior cast of the brachial valve ; showing a portion of the broail area of contact, the plat- 



form scars, with the diverging anteriin- ridges. 

 Niagara limestone. Rising Sun, Ohio. 



1. The iiitei'ior of a brachial vnlve, from a gutta-percha cast of a natural i;npression. The cre.si'entic 



fulcrum is exceedingly strong and the platform very obscure. 



8. 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 -g-roove and ci'escent. 



9. The interior of a brachial valve, with sharply defined terminal scars and anterior ridges. From 



a gutta-perch.a cast. 



10. An internal cast of a brachial valve ; showing, in the matrix, the impression of the cardinal area. 



The pliitl'orm scars are accompanied by scarcely any thickening of the .shell. 

 Niagara limestone. 6-rafton, Wisconsin. 



MONOMERELLA OVATA, Var. LATA, WllitcaveS. 



11. The exterior of a pedicle-valve. Fi-om the original specimen figured by Whiteaves (Palaeozoic 



Fossils, vol. iii, pt. 1, pi. 2, fig. 2a). 



12. A portion of the interior of a pedicle-valve. Prom Whiteaves' oi-iginal (op. cit., pi. 8, fig. 2). 



Guelph limestone. Durham, Ontario. 



MONOMEKELLA OVATA, WlliteUVeS. 



View from the lu-achial side of a fine specimen retaining the valves in conjunction. 



Profile of the same. From Whitbave.s' original specimen (op. cit., pi. 8, figs. 1, la). 



The interior of a pe<licle-valve ; showing the broad cardinal ai-ea and deltidial slope, the shallow 

 umlional chambers, the deep cardin.al groove and lateral scars of the crescent, an<l the sligli'ly 

 elevated anterior edge of the platfoi-m. Fi-om Whiteaves' original specimen {op. cit. pi ■■>, 

 fig. IK). 



Guelph limestone. Durham, Ontario. 



