THE DECAPOD CRUSTACEA. 



207 



converted into the young crab. This is merely one, and by 

 no means one of the most complex, of the life-histories of 

 the Crustacea, but it is one which can generally be easily 

 studied. In Fig. 59 another larval stage, one which is 

 common among long-tailed Decapods, is represented. Its 

 great interest lies in the resemblance to the opossum-shrimp, 

 especially as regards the shape of the legs. 



KEY FOE, THE IDENTIFICATION OF CRABS DESCRIBED 



IN THIS CHAPTER. 

 Order DECAPODA. 



II. REPTANTIA (see p. 163), Brachyura, or crabs in the narrow 

 sense, including forms with short antenna, which, like the eyes and 

 an tommies, are placed in sockets. 



Carapace triangular with \ 1. Fam. Oxyrhyneha 

 rostrum, legs long . / (spider-crabs). 



Carapace broad, arched 

 in front, and narrow 

 posteriorly 



d l 

 w V 2. 



Fam. Cyclometopa. 



1. Fam. Oxyrhyneha. 



Chelipeds not 

 markedly dif- ^ 

 ferent from 

 other legs . 



Chelipeds much 

 shorter and 

 stouter than 

 other legs, 1 

 which are 

 very slender 



Rostrum with diver- / Maia 

 . \ 



gent horns Maia 



Rostrum with conver- 

 gent horns, hollowed \ 

 Beneath-Jfyo* 



squinado, with 

 prickly body. 

 In H. araneus the cara- 

 P a f? " oi contra cted 

 behmd the P~t-orbital 

 . T Processes 

 I In H. coarctalus it is con- 

 tracted behind these. 



Carapace sub-triangu- 

 lar, nearly as broad 

 as long, orbits elon- 

 gated Inaclius 



Carapace an elongated 

 triangle with long 

 rostrum Steno- 

 rkynchus 



Between tide-marks I. do- 

 rhynchus, with three 

 spines on the gastric 

 region, is the only 

 species found. 



Between tide-marks oc- 

 curs S. phalangium, 

 in which the rostrum 

 is shorter than the 

 stalk of the antennae. 



