PLATE IV B. 



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



b. Deltidlal slope. m. Median scars. 



c. Deltidial ridg-es. n. Anterior scars. 

 ca. Cardinal area. , o. Lateral scars. 



cr. Crescent. q. Crown of crescent. 



d. Areal borders. r. Side of crescent, 

 h. Cardinal buttress. t. Transeverse scars, 

 i. Umbonal chambers. u. Pallial sinuses. 



j. Platfoi'm. X. Umbo-lateral scars. 



TRIMEEELLA, Billings. 



Page 33. 



Trimekella Lindstr(emi, Dull. 



Fig-. 1. Ttie interior of an impei'fect pedicle-valve ; showing- the deeji excavation at the base of the del- 

 tidium in the place usually occupied by the cardinal buttress. 

 Aymestry limestone. Island of Gotland. 



Trimerella grandis, Billings. 



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

 Fig. 3. The ojiposite side of the same. 



Guelph limestone. Gait, Ontario. 

 Figs. 4, 5. Transverse sections, showing the sti'ucture of the platform. 



Trimerella acuminata, Billings. 



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

 scars of the crescent and the excavate cardinal butti-ess. From a gutta-pei-cba impression of 

 a natural cast. 



Niagara limestone. Port Byron, Illinois. 



RHINOBOLUS, H.^ll. 



.«■!!■■ "i 

 . ,, , Page U. 



Rhinobolus Galtensis, Billings. 



Fig. 7. The interior of a pedicle-valve ; showing the narrow deltidium, broad deltidial i-idges and the 

 small, imperfectly developed platform. The drawing is made from a gutta-percha impression 

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

 Guelph limestone. Gatt, Ontario. 

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



Guelph limestone. Elom, Ontario. 

 Fig. 9. The intei-ior of a larger brachial valve ; drawn from the specimen figureil by Whiteaves on plate 

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



Guelph limestone. Hespeler or DurTiam, Onta7'io. 



Rhinobolus Davidsoni, s^j. nov. 



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 platform, the crescent and the 



transverse muscular scars. 



Niagara limestone. Grafton,. Wisconsin. 



