150 A HISTORY OF RECENT CRUSTACEA 
from its companions by the large and long flagellum of 
the second antenne. Hippa emeritus (Linn.) is regarded 
by Mr. J. E. Ives as a very variable species widely distri- 
buted on the east and west coasts of North and South 
America. It is used, he says, by the fishermen for bait, 
and large numbers are dug from the sand. It is not un- 
likely, as suggested by Milne-Edwards, that Hippa tal- 
poida, Say, the ‘ mole-like ’ Hippa, is the same species. It 
was upon this that Professor S. I. Smith made his obser- 
vations at the United States’ Biological Station at Wood’s 
Hole, Massachusetts, in the summer of 1875. He was 
there able to obtain a nearly complete series of the post- 
embryonal stages, and has since elaborately described the 
second, third, and last zoéa forms, and the succeeding me- 
galopa condition. Some of his figures are reproduced on 
Plate IV. He observed that the adults preferred a very 
narrow zone of the shore, at or very near low-water mark, 
where they lived gregariously, burrowing in the loose and 
changing sands. 
‘The smooth, oval form of the animal,’ he says, ‘ with 
the peculiar structuie of the short and stout second, third, 
and fourth pairs of thoracic legs, enables them to burrow 
with far greater rapidity than any other crustacean I have 
observed. Like many other sand-dwelling crustaceans, 
they burrow only backwards; and the wedge-shaped pos- 
terior extremity of the animal, formed by the abrupt bend 
in the abdomen, adapts them admirably for movement in 
this direction. When thrown upon the wet beach, they 
push themselves backward with the burrowing thoracic 
legs, and by digging with the appendages of the sixth 
segment of the abdomen slightly into the surface, direct 
the posterior extremity of the body downward into the 
sand.’ 
The second antennz are generally held between the 
second and third maxillipeds, with the peduncles crossed 
in front, and the flagella curved down and entirely round 
the mouth so that the setae with which they are densely 
armed all project inward. Their function is not un- 
reasonably supposed to be that of removing objectionable 
