PLATE IV D. 



Leg-enil. 



Fig. 

 Fig. 



Fig. 



Fig. 



a. 



h. 

 cc. 



eg-- 

 cr. 



d. 



i. 



.i- 



Deltidiiim. 

 Deltidial slope. 

 Cardinal area. 

 Cardinal groove. 

 Crescent. 

 Areal borders. 

 Umbonal chambers. 

 Platform. 



m. Median scars. ^ 



n. Anterioi' scars, 



o. Lateral scars, 



p. Postmedian scars, 



q. Ci'own of crescent. 



r. Side of crescent, 



u. Pallial sinuses or Hdges (?). 



MONOMERELLA, Billings. 



Page 40. 

 MONOMERKLLA KiNGI, .Sp. UOV. 

 pedicle-valve ; showing the very short umbonal chambei's and the shai'ply 



1. An intei'iial cast of 

 defined musculai- imjiressions 



2, The opposite side of the same specimen ; showing the intei-nal characters of the brachial-valve. 

 Niagara limestone. Hawthorne, Illhiois. 



MONOMERELLA, Sp. ? 



li. 'J'lie inner side of a specimen retaining the stiell, believed to be a brachial valve of some .species 

 of this genus. This specimen is considei'ed by Wiutbave.s as the pedicle-valve of RMnohohis 

 GaUiMsls, Billings. Should Mr. Whiteaves' opinion pi-ove correct, it will probably be neces- 

 sai-y to remove Billings' species to some othei' genus. 



4. The exterior of the same siiecimen. 



Guelph limestone. Q-alt, OntaTW. 



MONOMERELLA GrEENII, sp. IIOV. 



Fig. 5. An internal cast of a jiedicle-valve ; showing the extremely small umbonal chambers and the 

 sharply defined crescent, cai'dinal groo\'e and lateral scars. 

 Niagara limestone. 6-rafton, Wisconsin. 



Fig. 6. An interioi- cast of the brachial valve ; showing a portion of the broad area of contact, the plat- 

 form scars, with the iliverging antei-ior lidges. 

 Niagara limestone. Rising Sun, Ohio. 



Fig. 7. The interior of a brachial v^lve, from a gutta-pei'cha cast of a natural impression. The crescentic 

 fulcrum is exceedingly strong and the platform very obscure. 



Fig. S. An intei-nal cast of a pedicle-valve ; showing the very bi-oad cardinal margin and its lateral exten- 

 sion ; also the faint umbonal cavities and the consxiicuous cardinal gi-oove and crescent. 



Fig. 9. The interior of a bi-achial valve, with sharply defined terminal scars and anterior i-idges. From 

 a gutta-peri:ha cast. 



Fig-. 10. An internal cast of a brachial ^'alve ; showing, in the matrix, the impression of the cardinal area. 

 The platform scars are accompanied by scarcely any thickening of the shell. 

 Niagara limestone. Criufton, Wiscoiisin. 



MONOMERELLA ovATA, vav. LATA, Whiteaves. 



Fig. 11. The exteiior of a pedicle-valve. From the original specimen figured by Whiteaves (Palaeozoic 



Fossils, vol. iii, pt. 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, WlliteavCS. 



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



Fig. 14. Profile of the same. From Whiteaves' original specimen (op. cit., pi. 8, figs. 1, la). 



Fig. 15. The interior of a pedicle-valve ; showing the broad cardinal area and deltidial slope, the shallow 

 umbonal chambers, the deep cardinal groove and lateral scars of the crescent, and the slightly 

 elevated anterior edge of the platform. Fi-oin Whiteaves' original specimen (op. cil. j-i. ■'-^, 

 tig. 16). 



Guelph limestone. Durham, Ontario. 



