552 



Forty-fifth Report on the State Museum. 



Trimerella, Billings. 1862. 

 (Plate 2, Figs. 9-12.) 

 Synonym; Gotlandia, Dall. 1870. 

 Shells thick ; outline ovate. 



Pedicle-valve with an erect and straight umbo, which is usually 

 solid for the greater part of its length, but double-chambered 

 toward its base ; cardinal area very prominent ; deltidium broad ; 



Fig. 245.— Pedicle valve of Trimerella. Fig. 246.— Brachial valve of Trimerella. 



After Davidson and King. 



deltidium. 



deltidial slope. 



deltidial ridges. 



areal borders. 



cardinal c«llosities. 



cardinal facet. 



lozenge. 



cardinal buttress. 



umbonal chambers. 



platform. 



platform vaults. 



median plate. 



median scars. 



anterior scars. 



lateral scars. 



post-median scars. 



crown | 



side >• crescent. 



end ) 



transverse scars. 



archlet (vascular sinuses). 



sub-cardinal scars. 



umbo-lateral scars. 



e, cardinal sockets. 



j. platform. 



fc, platform vaults. 



I, median plate. 



m, median scars. 



n, anterior scars. 



o, lateral s^ars 



p, post-median scars. 



q, crown ) 



r, side V crescent. 



s, end ) 



U transverse scars. 



u, archlet (vascular sinuses). 



v, cardinal scars. 



w, sub-cardinal scars. 



deltidial ridges more or less conspicuous; deltidial callosities 

 slightly developed ; cardinal slope well-defined. Crescent sharply 

 incised over its summit, but faint toward the sides, where it is 

 connected with the broad lateral and terminal scars, which are 

 not so distinctly outlined as in the allied genera. Platform long, 

 narrow and strongly developed; platform vaults tubular, the 



104 



