13 



Gerstascker and Ortmann, Malacostraca iu Bronn's Klassea und OrJnungen des Thier-ReichS' 

 Spence Bate, Beport on the Challenger Crustacea Macrura, Introduction. 

 Stebbing, A History of Crustacea (luternational Scientific Series). 



II. Classification of the Decafoda. 



Altlioufjli the views of Boas, who divides the Crustacea of the Malacos- 

 tracous Order Decapoda into two suborders Xatantia and Rejifantia, have much 

 to commend them, yet I prefer to follow Milne Edwards I. and Dana (from 

 whom also DeHaan is not essentially divergent) who recognize three principal 

 groups of Decapoda, namely, Macrura, Anomura or Auomala, and Brachijura. 



Of these three suborders the Macrura occupy the middle place, having 

 intimate connexions on the one hand with the AiiomaJa {Anomura) and on the 

 other hand with the Brachyura, while so far as can be seen at present, the two 

 latter groups {Anomala and Brachyura) are not connected with one another in 

 any other way but through the Macrura. 



The most obvious links between the Macrura and the Anomala (Anomttra) are (1) the 

 Thalassinoids, which are almost uuited with the Paguroids through the curious symmetrical 

 hermit-crab Pijlocheles, and (2) the TJroptychoids, which, through Ptychogaster, have a less 

 striking connexion with the Astacoids. On the other hand the interval between the Macrura and 

 Brachyura is almost bridged by the deep-sea Dromioid genera Homolodromia and Archnodromia. 



The three suborders of Decapoda are thus defined : — 



Suborder I. Macrura. Body elongate. Abdomen as well developed as, 

 or even better developed than, the cephalothorax, behind which it is more or 

 less completely extended and beneath which it is never permanently flexed, and 

 endinof iu a large symmetrical tailfan the lateral lobes of which (caudal swim- 

 merets) are almost without exception foliaceous. Front not joined with the 

 epistome. Thoracic sternum usually narrow : if broad, the last segment is not 

 independently movable. The genital ducts never open on the sternum. The 

 antenna! peduncle commonly, though not universally, carries a movable exopodite, 

 which is generally foliaceous. 



Suborder II. Anomala or Anomura. Abdomen less well developed than 

 the cephalothorax : although in a few exceptional forms it is elongate and 

 symmetrical and extended in a straight line behind the cephalothorax, it is as a 

 rule either (1) flexed or rolled on itself, or (2) flexed against the stenuim, or (3) 

 coiled in a spiral, in which last case it is more or less soft and asymmetrical. It 

 is only exceptionally that the 6th abdominal somite is destitute of appendages 

 homologous with caudal swimmerets. The front is not united with the epistome 

 across the ophthalmic somite. The last thoracic segment is independent, the 

 last segment of the thoracic sternum, when not atrophied, being movable. The 

 genital ducts never open on the sternum. If the autenual peduncle carries an 

 exopodite, this is never foliaceous. 



