150 A HISTOEY OF EECENT CRUSTACEA 



from its companions by the large and long flagellum of 

 the second antennae. Jlippa 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 IlippO' tcd- 

 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 zoea 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 antennas 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 setas with which they are densely 

 armed all project inward. Their function is not un- 

 reasonably supposed to be that of removing objectionable 



