4<10 
MQLLUSCA. SIPHONIDA, 
A A. Destitute of a secreted calcareous tube, 
a. Ligament external. 
Pholad^. With accessory valves, or gaping ven- 
trally. 
Pholas. 
Gastrochsena. 
SoLENiD^. No accessory valves ; gaping only at the 
extremities. 
Solen 
Sanguinolaria. 
Hiatella. 
Panopsea. 
(Glycemeris) 
a a. Ligament internal. 
Mya. 
Lutraria. 
Sphenia. 
Pandora. 
Galeoma. 
