ARTHROPOD A. 85 



to considerable modifications. The teguraentary skeleton varies 

 from being thin and flexible to a hard and solid calcareous 

 crust. 



In their development the Podophthalma vary greatly ; in some 

 reproduction is direct, but in others, and more generally, the 

 young emerge from the egg as a Naiiplius or a Zoea, the Nauplius- 

 stage, however, being sometimes passed in the ovum. A later 

 larval form is the Megalopa. The changes are effected gradually, 

 and while the animal is still comparatively minute ; and they do 

 not appear to be correlated with other characters. 



Branchiae external STOMATOPODA. 



Branchiae enclosed in the thorax DECAPODA. 



Order I. STOMATOPODA. 



STOMAPODA. ANOMOBRANCHIATA. 



Branchiae external, either placed beneath the abdomen or at- 

 tached to the thoracic legs, occasionally rudimentary or wanting. 



The carapace covers the whole or only a part of the thorax, 

 and is generally thin and flexible. The abdomen is elongate, and 

 terminates in a natatory tail. The gnathites are confined to a 

 pair of mandibles, two pairs of maxilla?, and a pair of foot-jaws, 

 which are sometimes rudimentary, or are converted, as well as 

 the seven succeeding pairs of limbs, into natatory feet. 



The branchiae consist of numerous minute cylinders, closely 

 arranged on larger cylinders ; they are wanting in Mysis, 



Leuciferidas compose the " tribe " Aplopoda of Dana. They are 

 placed in the Macrura by Clans, who confines this order to the 

 Squillidae. The remainder are referred as a "suborder" to the 

 Schizopoda of Latreille. Nebalia, formerly referred to Phyllo- 

 poda, is sometimes doubtfully placed here; it is a transition-form 

 of a special type. 



Mysidce. Euphausia. Sguillida. 



Mvsi Squilla. 



Sla. Lopkogastnda. G 4 onodactylus> 



Petalophthalmus. Gnathophausia. Coronis. 



Lophogaster. Leuciferida. 



EuphausiidcB. Chalaraspis. Leucifer. 



Thysanopoda. Sergestes. 



Nebalia. 



