xr PHYLUM ARTHROPODA W9 



are both largo; the former arc not sunk in pits, and the antennae 

 usually have a scale-like extipodite (squame). 



Included among the Macrura are (a) swimming forms — Pencms 

 and Palwmon (Prawns), Crangon (Shrimps), Lucifer, etc. ; and (b) 

 creeping forma — Homarus (Lobster), Astacus, Astacopsis, Para- 

 nephrops, Oamiarm (Fresh-water Crayfishes), Palinnrus (Rock- 

 lobsters), Scyllarus, etc. (Figs. 465, 466). 



Sub-order 2. — Anamura. 



Decapoda with the abdomen more or less reduced, usually held 

 in a flexed position, and not provided with such a well-developed 

 tail-fin as in the Macrura. 



In most respects the Anomura are intermediate between the 

 Macrura and the Brachyura. Examples are the Hermit-crabs — 

 Pag a rus (Fig. 467), and other genera, the Cocoa-nut crab — Birgus 

 — Galathca, Hippa, Porccllana, etc. 



Sub-order 3. — Brachyura. 



Decapoda in which the abdomen is greatly reduced, shorter 

 than the cephalothorax, and permanently flexed beneath it. The 

 antennules and the eyes are both capable of being retracted, 

 into cavities. There is a metamorphosis comprising zona and 

 megalopa stages. 



Including the true Crabs such as Cancer, Maia, Grapms, etc. 

 (Figs. 468, 469). 



Division 4. — Hoplocarida. 



Malacostraca in which the carapace does not coalesce with 

 at least the last four thoracic segments, so that the cephalothorax 

 is relatively short. In front of the head proper are two movable 

 segments, one bearing the stalked eyes, the other the antennules. 

 The branchiae are borne on the abdominal appendages. The 

 heart is elongated. There is a metamorphosis, but a nauplius 

 stage is not known to occur. 



Order Stomatopoda. 



This, the only order of Hoplocarida, includes Squilla (Fig. 470), 

 Gouodactylvs, and other genera. 



Syteinatic Position of the Examples. 



The genera Apus and Lepidurus belong to the family Apodidw 

 of the order Notostraca of the sub -class Branchiopoda. 



The foliaceous character of the swimming-feet is alone sufficient 

 to assign them to the Branchiopoda, and the large number of seg- 



