INTRODUCTION. 



"In the vast extension .... which marine Zoology has for some lime past been receiving, 

 some retardation in the stream of discovery may not be unwelcome to the systematise 

 Familiar forms which would otherwise amply repay a thorough reinvestigation are apt to 

 be thrust on one side, when striking novelties are for ever appealing to be introduced". 

 Th. R. R. Stebbixg, Stalk-eyed Crustacea Malacostraca of the Scottish National Antarctic 

 Expedition. Transact. Roy. Soc. Edinburg, v. 50, prt 2, n" g, 1914, p. 253. 



With Prof. Weber's kind permission and the ready consent of Dr. Ihle I have been 

 entrusted with the task of working up a part of the Brachygnathous Crustacea Decapoda of the 

 "Siboga" Expedition. The present paper deals with 5 families: Hymenosomidae, Retroplumidae 

 (= Ptenoplacidae), Ocypodidae, Grapsidae and Gecarcinidae, v i z. the bulk of the large group 

 commonly known as Catometopous Crabs. 



The families enumerated yielded 68 species in all and only 4 of them are new to science. 

 This fact may seem disappointing, in view of the large series of new forms, continuously 

 appearing in almost every larger group of marine Evertebrata secured by the expedition, but 

 is not to been wondered • at. Firstly the Ocypodidae, Grapsidae and Gecarcinidae are, as is 

 well-known, inhabitants of the beach, of mouths of rivers and brooks, and of the jungle near 

 the shore, and the "Siboga", devoting most of her labour to deep-sea working, only occasionally 

 collected terrestrial and fresh-water animals. And secondly the scarcity of new species may readily 

 be explained by the very habits of the three families, the species of which are generally largely 

 represented in such collections as are gathered by naturalists of tropical regions, who have no 

 particular means at their disposal of investigating the deeper and more inaccessible regions of 

 the sea; and collectors as Brock, Storm, Semper, Kukenthal a. o. have made us acquainted 

 in more recent years with a rather large number of new species of the said families, so that 

 the chance of discovering novelties in this regard is small. 



In the present paper it are not the new forms which are laid stress upon, but rather 

 it is a synopsis of all the known Indo-Pacific species, together with keys to genera and species, 

 that is aimed at. Alcock's classical work "Materials for a Carcinological Fauna of India" and 

 eventually n" 6 in: Journ. As. Soc. Bengal, v. 69, prt 2, 1900, only deals strictly with Indian 

 (or rather British-Indian) species, and is only to a limited degree suited to any naturalist who 

 attempts the determination of Catometopous crabs from the East-Indian Archipelago. The 

 literature on the subject is so very much scattered, that a general review on the carcinological 



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SIBOGA- EXPEUITIE XXXtXi'. I 



