NATURAL SCIENCES OP PHILADELPHIA. 123 



spade. The holes are usually just large enough to admit the 

 hand a little way, and pass in every direction downwards ; may be 

 straight or tortuous, and from a few inches to a yard or more in 

 depth ; two or three feet ma}' he an average excavation. Usually 

 the sand is heaped up about the entrance, and forms quite a con- 

 spicuous mound. It is apparently simply pushed out in most 

 instances ; but in one instance that I examined with particular 

 care, this was not the case. The hole was in perfectly dry and 

 drifting sand, and all around, at varying distances, from a foot to 

 over a j^ard from the entrance, lay little separate piles of fresh 

 wet sand brought up from below ; a ditferent set of tracks leading 

 to each heap. This showed that the animal had repeatedly 

 brought up an armful of sand, and dumped it at some distance. 

 The holes, I may add, are almost invariably placed above ordinary 

 high-water mark, mostly in the flat dry shingle separating the 

 beach proper from the adjoining sand-drift dunes. A small pro- 

 portion of the crabs live in the sand-drifts still back of this, and a 

 few others come about the houses near the fort, digging in odd 

 corners, and to all intents and purposes replacing the house-rats. 

 Their remarkable swiftness of foot is well known ; and when 

 brought to bay, their pugilistic attitudes and actions are as 

 noticeable as is the sly cat-like aspect they present when crouching 

 closely, in hopes the intruder will pass them unnoticed, or in hang 

 in wait for prey. The large claws are of porcelain-like whiteness 

 and hardness, and capable of inflicting a wound not to be over- 

 looked in a moment ; but the general covering is so soft that the 

 animals are disabled, or even killed outright, by being simply 

 dropped upon the hard sand from the height of a man's head. 

 The young, which are at first spotted, and bear little resemblance 

 to the adults except in shape, begin to appear in the latter part 

 of April ; and they are an inch or more wide before they begin to 

 assume the general dull yellowish color of the adults. These 

 crabs are put to no use, except to afford excellent sport to boys 

 and boyish men, who bait them with their canine companions. 



Pinnotheres ostraeum. 



The oysters furnish the usual numbers. 



Persephona punctata. 



Common, on the sand-bars, &c. 



1871.] 



