INTRODUCTION. 



In the present paper two families, Goneplacidae and Pinnotheridae, are dealt with, so 

 that now the whole group of the Catometopons Crabs has been worked out. 



The members of these families are for the most part little known, partly because of 

 their usually small size and partly on account of the fact, that a great many species have a 

 commensalistic mode of life, with Lamellibranchs in the majority of cases, but also in Holothu- 

 rians, Echinoids, Ascidians, and in tubes of Annelids. They may be very scantily represented 

 or even entirely absent in large coUections, so the " Challenger" and the "Valdivia" obtained 

 each only ii species, the "Sealark" expedition in the Indian Ocean (1905) a single species. 



The materials of the "Siboga" expedition proved to be very rich in this respect, and 

 may easily stand a comparison with the large collection, made by Mortensen in the Gulf of 

 Siam and examined by Miss Rathbun (19 10). The two families taken together yielded 50 species, 

 15 of which turned out to be new, and 3 of these represent as many new genera. 



In a rapid glance over the results obtained we first take the Goneplacidae. 



These are represented in the collection by 37 species, 12 of which are new to science, 

 while 2 new genera are established. The genus Litochcira Kinahan yielded six species, three 

 of which are new. The subfamily Goneplacinae, besides by two already known species of 

 Goneplax, is represented by a new form of the remarkable New Zealandian genus Ommato- 

 carciiius White. Of the subfamily Prionoplacinae^ which is nearly e.xclusively American, the 

 little known Homoioplax haswclli (Miers) Rathbun was found back; the genus Speocai'ciniis 

 Stimpson, which was known only from the Atlantic and Pacific coasts of America, is represented 

 by a new species; and finally a genus {Lophop/ax) has been established on a new species. Of 

 the subfamily Rhizopinae a whole series of new or little known species were obtained, numbering 

 18 in all; of these 5 new species (Typhlocarcinops Rathbun 2, Xenophthalmodes Richters i, 

 Typhlocarcinodes Alcock 1, Hephthopelta Alcock i) belong to already known genera, a 6* 

 species represents a new genus, Parasehvynia. 



Of the Pinnotheridae (13 species) the rich' genus Pinnothcrcs is of course abundantly 

 represented ; of the 8 species obtained I am satisfied to refer 6 to already known species, while 

 2 others are apparently new; the discrimination of the various species is often most trouble- 

 some. In the subtamily Asthenognathi)iae a genus, Apiianodactylus^ is proposed to receive a 



SIBOGA-F.XPEDITIE XXXIX <: 



ü483e 



