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 is thus 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 Caiman (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 Hapalocarcinidae. 

 The galls examined by Caiman 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 Caiman 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. Caiman was kind enough 

 to point out to me the interest attaching to the natural history and 

 reproduction of the Hapalocarcinidse. 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 ccespitosa and Seriatopora hystrix, both belonging to the same 

 family, the Pocilloporidse, 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 



