332 ME. J. E. HENDERSON— A CONTEIBUTION 



deeply hollowed out by the body of the crab, is exemplified in most of the reef -dwelling 

 species, aud the canals of larger fixed Sponges afford a shelter to species of Polyonyx, 

 Alpheus, and Gebiopsis. The larger species of Alpheus, and Gonodactylus glaber, are 

 often found ensconced in short tunnels, bored through the coral probably by Lithodomi 

 or other molluscs, and when captured the Stomatopod has the habit of alternately flexing 

 and extending its tail with considerable rapidity and force. Certain representatives of 

 widely separate families, e. g. CEthra scruposa and Ebalia fallax, have the carapace very 

 irregularly elevated or even pitted, so that they bear an undoubted resemblance to 

 pieces of eroded coral, and, as they move but slowly, this adaptation to their environment 

 must often aid in their protection. But specially interesting in many of the species 

 are the colour-markings, which probably, in most cases, are protective in their nature ; 

 and it may be added that an examination of dry or spirit specimens gives one but a 

 meagre idea of the vivid tints which characterize many of the reef-dwellers during life. 

 The colours which occur most frequently are purple, brown, and red, either uniformly 

 diffused over the surface of the crab, or restricted so as to form spots or bands. A 

 modification of the latter type is seen in such diverse forms as Zebrida Adamsii, Cyclo- 

 wantlms lineatus, Eupagtirus zebra, and Galatliea elegans, in which there is an arrange- 

 ment of dark, radiating, or subparallel lines, on the carapace and legs. A hint as to the 

 possible use of these bands was afforded by a small semitransparent Lamellibranch 

 {Avicula zebra, Reeve), with black radiating lines on its shell, which is met with 

 adhering by its byssus to a hydroid {Aglaop>henia urens, Kirchenpauer) * ; in this case 

 the lines so exactly simulate the short lateral ramuli of the hydroid that the shell is 

 with difficulty recognized, even by a practised eye. In all probability the above- 

 mentioned crustaceans live on the stems of Gorgoniae, Hydroids, or similar organisms. 

 The Cancroid genera are more often brightly coloured than are those of other 

 groups, and they include the species which are found in greatest numbers on the reef. 

 It may be stated generally that the inactive forms are those most commonly disguised, 

 either by the presence of foreign objects or by colour adaptations, while their more 

 active neighbours, such as the Portunidae and many Macrura, are, as a rule, of more 

 sombre hue, but are more frequently armed with sharp spines, probably for defensive 

 purposes, while those which seek safety in tunnels or burrows are often pale in colour, 

 with their outer shell of thin texture. Before leaving this subject I may refer to a 

 structural feature which is very noticeable in many species, more especially among the 

 Cyclometopa, viz. the strong spoon-like excavation of the claws, which possibly enables 

 these crabs to obtain a firmer hold of, and break off, the smaller coral branches when 

 in search of food. 



On the subject of geographical distribution there is little to be said, apart from the 

 notes which appear in the body of this paper. The Indian Crustacean fauna is apparently 

 very similar to that of a great portion of the Indo-Pacific area, and it is doubtful whether 

 there is a single genus confined to or specially characteristic of India. The distribution 



* I am indebted to Mr. Edgar Smith aud Mr. Kirkpatrick, of the British Museum, tor the identification of the 

 mollusc and hydroid respectively. 



