MORSE: OBSERVATIONS ON LAMELLIBRANCHS. 
177 
SO alternating. The syphcjnal walls are thin and niottletl with 
minute black blotches. 1 have never observed the valve in the 
adult state, though in the young it is quite conspicuous (Fig. 31, 
a). When the shell rests on its side the syphons turn upward 
Fig. 31. — Venus mercenaria LinD6. 
at right angles to the long diameter as in Pandora. In the very 
young shell, as shown in Fig. 31, a, the hinge margin posterior to 
the beak is straight. The shell is marked with high concentric 
ribs. The syphons are long and narrow, the valve is conspicuous 
and light yellow with black mottlings. 
GEMMA GEMMA (Totten). 
Fig. 32. Length, .5 mm. 
This beautiful little purple shell is so abundant along the 
coast that some beaches are tinged purple by their number. 
The beach at Annisquam, Cape Ann, is rendered distinctly 
purple by the thousands of these shells left by the receding tide. 
