830 QUADRULA 
A rather small member of the plicata group, always much 
inflated, decidedly quadrate and having delicate, almost hori- 
zontal folds. ‘The posterior ridge is always full. I have seen 
a specimen without locality, which I refer to this, in which 
the folds are almost wanting. <A shell of trapezoides before 
me is shaped almost exactly like neislerii, but it has only a few 
short folds in front of the posterior ridge and a deep purple 
nacre. 
Group of Ouadrula trapezoides. 
Shell rhomboid, inflated, with a high posterior ridge; beak 
sculpture coarse, irregular corrugations swollen to nodules 
on the posterior ridge; surface sculptured on posterior half 
with oblique ridges, which are sometimes corrugated, and with 
strong corrugations on post-slope; beak cavities only moder- 
ately deep; nacre purple. 
Animal with the gills slightly rounded below, inner the 
larger throughout, free from the abdominal sac; palpi enor- 
mous, long ; branchial opening very large, finely papillose ; anal 
opening with fine papillz or crenulations. 
QUADRULA TRAPEZOIDES (Lea). 
‘Shell long rhomboid, subinflated to inflated, solid, inequilat- 
eral; beaks only moderately full and high, their sculpture con- 
sisting of a few decidedly nodulous corrugations; posterior 
ridge strong and high, often pinched up into a sharp angle, 
ending at the base of the shell in a point; anterior end a little 
narrowed and rounded: base line straight; post-dorsal area 
somewhat winged; posterior end obliquely truncated with a 
slightly curved outline; surface with a few oblique folds in 
front of the posterior ridge and on the posterior end there are 
curved folds; umbonal region with lengthened nodules ar- 
ranged in zigzagged patterns; epidermis brownish or black- 
ish; pseudocardinals ragged, radially split; laterals long; mus- 
cle scars large, the anterior ones filled with roughened nacre ; 
beak cavities moderately deep; pallial line remote; nacre pur- 
ple-red. 
Length 160, height too, diam. 65 mm. 
Length 108, height 67, diam. 43 mm. 
