36 Papers from the Department of Marine Biology. 
the influence of constant currents on the growth of coral by the forma- 
tion of galls and the modification in the shore of coral reefs. In the 
former case the current is produced by the respiratory movements of the 
crab. The recognition of the definite factor in gall production isthus due 
to this author. A description (and, in some cases, figures) of the galls 
formed in Seriatopora, Sideropora, and Pocillopora is given, but it is 
somewhat incomplete and not always correct in details. But the great 
merit of having pointed out the interest of the form belongs to Semper. 
Passing over one or two short notices of the genus, we come to a 
paper by Calman (2) which gives a thorough description of the external 
features of the adult female, from two or three individuals collected by 
A. C. Haddon in Torres Straits. An important part of this contribu- 
tion relates to the systematic position of the genus. In various points, 
particularly the structure of the third maxilliped, Hapalocarcinus occu- 
pies a very isolated position among the Brachyura Brachyrhyncha. 
These peculiarities it shares with Cryptochirus, another coral-inhabiting 
crab, which is discussed in the second part of this paper. The two 
genera are therefore united to form the family Hapalocarcinide. 
The galls examined by Calman were situated upon a species of Seria- 
topora; they are figured and described, but as preserved material alone 
was inspected not much of importance with regard to the biology could 
be added to Semper’s account. The series of individuals was too small 
for all points of structure to be examined. About the reproduction of 
the form Calman says: 
“The fact that each gall is inhabited by a solitary female, while the male 
is as yet unknown, would seem to indicate that the sexes are at first free-living 
and that it is only after impregnation that the female becomes imprisoned in 
a gall. The fact that the youngest gall observed is of ample size to contain 
a full-grown Hapalocarcinus tends to confirm this suggestion.” 
In the spring of 1913, when I was preparing to join the Carnegie 
Institution Expedition to Torres Straits, Dr. Calman was kind enough 
to point out to me the interest attaching to the natural history and 
reproduction of the Hapalocarcinide. During our stay at Murray 
Island, from September 22 to October 27 of that year, I was able to 
obtain an abundance of material and make some new observations on 
the biology. 
Hapalocarcinus lives in great numbers on the reefs of Murray Island 
at the north end of the Great Barrier Reef of Australia. It here forms 
galls on at least two species of branching Madreporarian corals, Pocil- 
lopora cespitosa and Seriatopora hystrix, both belonging to the same 
family, the Pocilloporide, and characterised by dichotomous branching. 
Both are widely distributed and dominant forms, but the former, a 
beautiful rose-coloured coral in life, is the favourite host of the gall- 
forming crab. In the still waters of the inner reef there is hardly a 
colony which does not bear at least one of the galls, while some show 
nine or ten in various stages of development. The ease with which the 
