﻿20 TRUNCILI.A * 



Truncili.a i.r.wisii Walker. 



"Male shell quadrate, suI)convi)ressed ; thick, solid ; dark 

 reddish-yellow, with faint, radiating- lines of green ; beaks lat- 

 erally ciMiipressed, eroded, but apparently only slightly ele- 

 vated above thie hinge-line, sculpture not seen; anterior end 

 regularly rounded, forming an obtuse angle at its junction with 

 the basal emargination, which is nearly straight ; dorsal line 

 curved ; posterior end slightly emarginate and terminating in 

 a broad biangulation, which projects slightly beyond the pos- 

 terior and basal lines ; a broad, flat groove extends from the 

 beaks to the basal emargination, widening and deepening as 

 it approaches the base ; posterior ridge prominent, rounded 

 toward the beak, but becoming flattened and obsoletely bian- 

 gulatcd as it approaches the posterior end ; immediately in 

 front of the median groove there is a strong anterior ridge, 

 which becomes more pronounced as it approaches the base, 

 where it terminates in an angle at the anterior end of the basal 

 emargination. it is more or less roughened by the accentua- 

 tion of the lines of growth, which elsewhere on the disk are 

 not very strongly developed ; dorsal slope concave behind the 

 posterior ridge ; interdentum rather long, narrow, rounded and 

 parallel with the hinge; pseudocardinals in the left valve, two, 

 the anterior very narrow, straight, directed obliquely forward 

 and slightly widening toward the anterior end. the posterior 

 triangular, the space between them triangular and extending 

 to the hinge ; in the right valve, two, the anterior smaller, but 

 well developed, the posterior long, triangular, the space be- 

 tween them narrow, direct and extending to the hinge-line, 

 the posterior tooth is separated from the interdentum by a 

 deep groove ; lateral teeth bent obliquely downward from the 

 hinge-line, two in the left valve and one in the right, large 

 and nearly straight ; anterior adductor impressions large and 

 deep, those of the protractor-pedis well marked, rather long and 

 narrow, below and slightly behind the adductor; anterior re- 

 tractor impressions small and on the base of the pseudocar- 

 dinal ; posterior adductor impressions large, semicircular ; those 

 of the ix)sterior retractors small, but well impressed, above 



