As Leda jeffreysi quadrangularis Dall, 1881
This turns out on comparison with specimens to be entirely unlike L. Jeffreysi, and I have not found anything like it. It is nearest pusio, and has the same concentrically finely undulate surface, but the basal pout and longest slope of hinge-line are posterior here, while, in pusio, both are anterior. I have not been able to satisfy myself that there was any ligament pit inside. There is a smooth interval between the two sets of teeth, but no pit, and no evidence that any ligament was attached there. It would belong to Seguenza's section Saturnia. The valve is 4.6 mm. in length, 4.0 mm. high, and the pair were probably 3.0 mm. in diameter.