DEPARTMENT OF MARINE BIOLOGY. 159 



are intersected by channels 6 or 8 feet deep, rendering their various parts 

 easy of access. There are also large holes which may be several hundred 

 yards in diameter and 20 feet deep, which, like natural aquaria, usually con- 

 tain representatives of 30 or 40 species of fishes, sometimes available for 

 study when rough weather renders it impossible to work to advantage else- 

 where. When both sea and tide are high, however, no place is so quiet and 

 free from tm'bidity that one may work under water with much profit. 



At a few points the edge of the main reef was accessible for a portion of 

 the time, yet dm'ing my stay in Pukoo (from July 3 to August 21) there was 

 no day on which the trade wind diminished sufficiently to permit free examina- 

 tion throughout its length of the rugged bottom just beyond the breakers 

 where species most abound. How much of interest lies there may be inferred 

 from the fact that 50 species of fishes, represented in all by many hundreds 

 of individuals, were seen at one station within an hour and within a radius 

 of little more than 50 feet. 



Beyond the breakers the bottom is essentially smooth rock, bearing upon 

 it sparsely scattered colonies of branching coral, and sloping gradually out to 

 deep water. It may be bare, covered by loose white sand, or by a thick, short 

 turf of algae, long, freely waving Sargassuryi or Didyota, for example, having 

 been obsen^ed at only a few places on the inner flat. Fishes do not appear 

 upon it by day in large numbers in proportion to its area. This region was 

 usually difficult to reach through the breakers with a small boat, but since 

 others more accessible were sufficiently rich and varied to provide profitable 

 emplojTnent for a longer period than was available for their study, the Umita- 

 tions prescribed by the weather were not as oppressive as might otherwise 

 have been the case. 



Advantage was taken incidentally of the opportunity to make a few ob- 

 servations upon Brachyura. 



Ocypoda ceratophthalma (Pallas) burrows in sandy beaches between tide- 

 marks. It comes out most freely by night, except perhaps on unfrequented 

 shores, where it is said to be less distinctly nocturnal in habit. The burrows 

 constructed by the creatures at different stages in their development vary 

 in form. The youngest dig simple vertical holes in the sand. Those of inter- 

 mediate size usually incline their main tunnel toward shore and from a point 

 midway in its length carry up a vertical shaft or chimney which they may 

 or may not leave closed at the surface, and in which they commonly rest, 

 as 0. arenaria of the Atlantic coast of America and the West Indies does 

 under like conditions. The burrows of the adults of 0. ceratophthalma are, 

 however, upon the whole rather more elaborate than those of 0. arenaria. 

 Some are like those constructed by crabs of medium size, but lack the vertical 

 chamber. Others descend spirally for about one complete revolution before 

 turning more or less sharply down and out to a point from 1 to 23/^ feet beneath 

 the surface. 



The course of the spiral in some burrows is clockwise, in others the reverse. 

 The first are dug by crabs with the larger chela on the right side, the second 

 by those which have it on the left. Both types of burrows are so firmly 

 stopped up with sand from the inside by their occupants, at a point about 

 as far down as the end of the first complete tm'n of the spiral, that one is very 

 apt to fail to follow the burrow farther, since the hardness of the bulkhead 

 may be little less than that of the undisturbed sand. When they are uncovered 

 both right-handed and left-handed individuals are found in the bottom of 

 the burrow with the large claw outermost. 



Sometimes a burrow is occupied by more than one individual. A large 

 hole with a small chimney had two tenants, of which the smaller in the upper 



