VI TIIALASSINIDEA — ANOMURA 1 67 



right order, rather goes to show that this is the primitive mode of 

 development in the- Decapoda, and that the disarrangement in the 

 order of appearance of the segments, both in the Squillidae and in 

 the Loricata and other Decapods, has been independently acquired 

 in the two cases to meet the needs of the larval existence. 



Fam. 1. Palinuridae. — The cephalothorax is subcylindrical, 

 the eyes are not enclosed in separate orbits formed by the edge 

 of the carapace, and the second antennae possess flagella. 

 Pallnurus, with P. elephas, the European Eock Lobster or 

 Langouste. lasus with two species in the Antarctic littoral ; 

 Fanulirus in the tropical littoral. 



Fam. 2. Scyllaridae. — The cephalothorax is depressed, the 

 eyes are enclosed in separate orbits formed by the edge of the cara- 

 pace, and the second antennae have flat scales in the place of flagella. 

 Scyllarus (Fig. Ill), with the European S. arctus ; Ihacus in rather 

 deep water with several species, chiefly found in the southern 

 hemisphere. 



Tribe 6. Thalassinidea. 



This tribe is included by some authors in the Anomura, and 

 held to be closely related to the Galatheidea, but the unreduced 

 abdomen is carried straight and unflexed, and gives a very 

 Macrurous appearance to the animal. The Anomurous char- 

 acters are the frequent reduction or absence of the antennal 

 scale, the fact that only the first two pairs of pereiopods are ever 

 chelate, and the reduced series of gills. The body is symmetrical, 

 but the first pair of chelae is always highly asymmetrical. The 

 posterior pairs of pereiopods, although small, are not character- 

 istically reduced as in the Anomura. The animals belonging to 

 this Tribe attain two or three inches in length, and generally 

 burrow in sand or mud either in the littoral zone or in deeper 

 waters; at the same time they can swim with considerable 

 activity by means of the pleopods. 



Fam. Callianassidae. — Callianassa suhterranea is common 

 at Naples, Gebia littoralis in the North Sea. 



Sub-Order 2. Anomura 



In this division are included the so-called Hermit-lobsters and 

 Hermit-crabs, in which the condition of the abdomen is roughly 

 intermediate between that of the Macrura and that of the Brachyura. 



