VI THALASSINIDEA—ANOMURA 107 
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. 
Palinurus, with P. elephas, the European Rock Lobster or 
Langouste. asus with two species in the Antarctic littoral ; 
Panulirus 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. 111), with the European S. arctus ; Lbacus 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 subterranea 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. 
