X, D, 1 Cowles: Tropical Crustacea, II 15 



Taytay along the beach in such regions as are inhabited by 

 Ocypoda. In fact I have never seen Myctiris longicarpus except 

 at low tide, and then only at a considerable distance seavi^ard 

 from the high- tide mark on exposed sand flats. When the tide 

 is low and the sand flats are uncovered, this Myctiris makes its 

 appearance in bands of almost countless individuals. They 

 move about like diminutive armies, reminding one somewhat of 

 the habits of certain species of fiddler crabs, but as soon as the 

 tide begins to flood they disappear, and I have never been able 

 to see them on the bottom, even with the aid of a water glass, 

 until the sand flats became exposed again. 



While Myctiris longicarpus is quite inconspicuous at a -dis- 

 tance of from 12 to 15 meters, it is very striking in appearance 

 at close range. The body, which is almost spherical in shape 

 and grayish blue in color, is of about the size of a large cherry. 

 The light-colored legs, including the chelipeds, are set rather 

 close to the body and are curved to conform with the spherical 

 shape of the animal. 



If one is fortunate enough to get close to a group of these 

 crabs, it is seen that while the individuals seem to be scrambling 

 along in a rather awkward and aimless manner, they all are 

 headed in the same general direction and are moving forward 

 as a unit. Sometimes, however, the group becomes separated 

 into two, after which each group may move in a different 

 direction. 



So far as I have been able to make out, these crustaceans do 

 not eat either dead or live crabs or fish. During their migrations 

 over the sand flats they are continually scooping up sand with 

 their chelipeds and smearing it over the mouth parts. Undoubt- 

 edly the latter manipulate the sand so as to extract the food, 

 and it is highly probable that Myctiris lives on the minute or- 

 ganisms and possibly minute pieces of decaying matter found 

 on- the surface of the sand flats. 



The most remarkable part of the behavior of Myctiris is the 

 rapidity with which it disappears when disturbed. An observer 

 may approach sometimes within from 6 to 10 meters of a group of 

 individuals (Plate II, fig. 1), when suddenly they seem to sink 

 into the sand. The disappearance seldom takes more than two 

 or three seconds and even by running one usually fails to reach 

 the group before it has disappeared. Occasionally, however, 

 when the sun is obscured and the approach is made carefully 

 and slowly, the observer may get close enough to watch the 

 migration and feeding. Then if a quick movement is made or 



