364 Bulletin American Museum of Natural History [Vol. LIII 
this sculpture may be inconspicuous or even wanting; and it very rarely 
appears until the shell is 40-50 mm. long. The interior is almost always 
white throughout in adult shells; rarely some violet stains appear near 
the posterior adductor sears. Young shells are often considerably 
stained with violet within, or rarely are largely jasper pink. The very 
strong cardinal teeth vary a good deal in details. The median cardinal 
of the right valve is strong and triangular, sometimes distinctly biramose, 
A-shaped, but usually the space between its sides is nearly or quite filled. 
The laterals are very weak. The nymphs are relatively small. The 
cavities of the beaks are very deep in large individuals, but quite shallow 
in the young. 
ene 146 mm.; height, 116 mm.; diameter, 62 mm 
120 91 fe 54 
Ogee ka) - 95 cy :O0 
4 94 ot 83 mb 49 
<6 75 z 66 67 66 50 
Y 73 : ‘ 68 i A7 
. 30 & ol f 22 (young) 
66 14 (er ian 14 a 72 fan 
Fig. 81. . Egeria congica (O. Beettger). Series of young shells. Natural size. 
In the earlier stages (Fig. 81) the height usually equals or sometimes 
exceeds the length; later the front and back ends grow faster than the 
middle, and the shell becomes relatively longer. The diameter is ereat- 
est in the earlier part of the mid-neanic stage, when it may exceed two- 
thirds of the length. In quite early neanic stages it is less inflated, the. 
diameter little more than half the length; and again in adult shells it is 
about half. Very old shells, such as the first measurement above, be- 
come strongly rostrate posteriorly, as usual in this genus. 
