PLATE IV B. 



Legend. a. Deltidium. k. Platform-vaults. 



b. Deltidial slope. m. Me<lian scars. 



c. Deltidial ridges.  n. Anterior scars, 

 ca. Cardinal area. o. Lateral scars. 



cr. Crescent. q. Crown of crescent. 



d. Area! borders. r. Side of crescent. 

 h. Cardinal buttress. t. Ti'anseverse scars, 

 i. Umbonal chambers. u. Pallial sinxises. 



j. Platform. x. Umbo-lateral scars. 



TRIMEKELLA, Hillings. 



Page 33. 



Tkimekella Lindstkujmi, Dull. 



Fig'. 1. The intericu' of an imperfect pedicle-valve; showing the deep excavation at the base of the del- 

 tidium in the place usually occupied by the cai-dinal buttress. 

 Ayniestry limestone. Island of Gotland. 



Tkimehklla grandis, Billing.^. 



Fig. 2. An internal cast of a portion of a small pedicle-valve. 

 Fig. 3. The opposite side of the same. 



Gueljih limestone. Gait, Ontoirio. 

 Figs. 4, 5. Transvei'se sections, showing the structure of the plattbrni. 



Tkimekella acuminata, Billings. 



Fig. 6. The interior of a pedicle-valve, somewhat restored about the umbo; showing the platform, lateral 

 scai-s of the i-i-escent and the excavate cardinal buttress. From a gutta-pei-cha impression of 

 a natural cast. 



Niagara limestone. Port Byron, Illinois. 



KHINOBOLUS, H.all. 



Page 41. 

 KniN0i50Lu.s Galtensis, Billing.s. 



Fig. 7. The interior of a jiedic-le-valve ; showing tlie narrow deltidium, broad deltidial ridges and the 

 small, imperfectly developed platform. The di'awing is ma<le from a gutta-percha impression 

 of a mould of the interior, the specimen being that (jriginally taken as the type of the genus. 

 Guelph limestone, (fait, Ontario. 

 Fig. 8. The interior of a small brachial valve. 



Guelph limestone. Elora, Ontario. 

 Fig. 9. The intei'ior of a larger bi'achial valve ; drawn from the specimen figured by Whiteaves on plate 

 8, tig. 3, Palfeozoic Fossils, vol. iii, pt. 1. 



Guelph limestone. Hespelei- or Durham, Ontario. 



RhINOBOLUS DaVIDSONI, .S[). IIOV. 



Fig. 10. A small pedicle-valve, showing the internal characters. From a gutta-percha impression of a 

 natui'al cast. 



Fig. 11. The interior of a brachial valve, believed to belong to the same species. 



Fig. 12. The interior of a larger brachial valve ; showing the undeveloped platfoi-m, the crescent and the 

 transverse muscular scars. 



Niagara limestone. Grafton, Wisconsin. 



