ECARDINES: INTERNAL CHARACTERS 



495 



of the Trimerellidae. A pair of " transverse " scars (t) occurs 

 in each valve between the " terminals " and the antero- 

 lateral edge of the " platform " {j). " Cardinal " (r), " suIj- 

 cardinal " {w), and " umbo-lateral " {x) scars also occur. The 

 median impression wliich covers the "platform" {j) consists of a 

 central, lateral, and usually an anterior pair of scars ; and the 

 impressions of the genital organs, according to Davidson and 

 King, lie medianly posterior to the " platform." The " platform " 



Fig. 323. — Trimerella. (After Davidson and King). A, Inner surface of pedicle-valve or 

 ventral valve : a, psendo-deltidium ; b, deltidial slope ; c, deltidial ridges ; d, areal 

 borders ; e, cardinal callosities ; /, cardinal facet ; ;/, lozenge ; i, nmbonal chambers 

 separated by cardinal buttress ; j, platform ; 1-, platform vaults ; /, median plate ; m, 

 median scars ; n, anterior scars ; o, lateral scars ; p, post-median scars ; q, crown 

 crescent ; r, side or lateral crescent ; s, end or terminal crescent ; f, transverse scars ; 

 u, archlet (vascular sinuses); w, sub-cardinal scars ; x, umbo-lateral scars. B, Brachial 

 or dorsal valve : e, cardinal sockets ; j, platform ; k, jJlatform vaults ; I, median 

 ]5late ; m, median scars ; «, anterior scars ; q, crov^^n crescent ; r, side or lateral 

 crescent ; s, end or terminal crescent ; t, transverse scars ; u, archlet (vascular 

 sinuses); v, cardinal scars ; iv, sub-cardinal scars. 



itself is a more or less conspicuous central calcareous elevated 

 area occurring in each valve, Init most developed in the dorsal ; 

 in some cases it is double -chambered with tul)ular cavities 

 ("platform vaults," Fig. 323, A, B, k), in others it is more or less 

 solid. It appears to have originated through a posterior shifting 

 of the central muscidar l»ands, that they might be inserted behind 

 tlic liver; at the same time a deposition (if slielly material, to 

 Ibrm fulcra to work the heavy valves, took place at these points. 

 The tunnelling -out of the platform was probably due to the 



