MAKINE CKUSTACEANS. 



PARTS IV.— VII. 



By L. a. Borradaile, M.A., Lecturer in Natural Sciences at Selwyn 



College, Cambridge. 



(With Plate XXII. and Text-figures 110—119.) 



IV. SOME REMARKS ON THE CLASSIFICATION OF THE CRABS. 



When Boas, in 1880', reorganised the classification of the Decapoda, abolishing the 

 distinction established by Fabricius between the Macrura and Brachyura, and dividing the 

 order anew into Natantia (Prawns and Shrimps) and Reptantia (Lobsters and Crabs), he 

 left the crabs (Brachyura) untouched, as a single tribe of the Reptantia. Within this tribe 

 he recognised two subtribes, one comprising the primitive Dromia-like forms, in which 

 the orbits, the abdominal limbs, the gills and other features recall the Macrurous tribes, 

 and the other containing all the rest of the true crabs. These subtribes he called respectively 

 Dromiacea and Brachyura genuina. Ortmann, however, elaborating Boas' scheme in 1896^ 

 took the step of dividing the Brachyura into three groups, each of which he made equal 

 in rank to the other subdivisions of the Reptantia {Astacidea, Loricata, etc.). These groups 

 were : (1) Boas' Dromiacea, under the name of Droniiidea, (2) the old division Oxystomata 

 established by Milne-Edwards for the crabs like Galappa and Leucosia which are modified 

 for life in sand, and (.3) the Brachyara, comprising the remainder of the crabs. In the 

 Brachyura he recognised, with some alterations, Milne-Edwards' divisions Oxyrhyncha (Spider 

 Crabs), Gyclometopa^ (Round-fronted Crabs, including Cancer-like genera), and Catometopa 

 (Square Crabs). 



It may be admitted that Ortmann was well-advised in establishing his three main groups 



of Crabs. If he be right — as, in the opinion of the writer of this paper, he is right — in 



regarding the Oxystomata as derived from the Dromiacea independently of the Brachyura 



genuina, then it is clearly misleading to retain Boas' arrangement, in which the Dromiacea 



' Boas, J. v., Kong. Danske Videmk. Sehk. Skriften (6), group of the same name. Later (Bronu's Tliierreich, Crust. 



I. p. 23. II. p. 1165) he returned to the use of the term Cyclometopa 



^ Ortmann, A. E., Zool. Jahrb. Syst. ix. p. 409. as including all its former genera, making it thus synonymous 



* Ortmann at first applied the name Cancroidea to this with Cancroidea. 

 group, his Cyclometopa forming only a part of Milne-Edwards' 



