ANOMOBRANCHIATA. ^3 



4. The legs have generally a largely developed palpus. These palpi 

 have a natatory form, being fringed with hairs or setae; yet, their 

 most important function is probably that of keeping the water in 

 currents over the body, in order to compensate for the want of true 

 branchia3. 



^ 5. One or two posterior pairs of thoracic legs are at times wanting, 

 either wholly (as in the Luciferidw), or with only the branchiae per- 

 taining to them present (as in the Euphausidce) . In some species, 

 the two posterior pairs of legs have at base a large curved plate, of 

 which a sac or cavity is formed under the thorax for carrying the 

 eggs (My since). 



6. The abdominal appendages may be of the full Macroural size 

 and number. Yet very often they are obsolete, excepting the caudal 

 pair. This caudal pair differs from those of the Macroural type in 

 wanting the articulation in the outer lamella; and, moreover, the 

 two lamellae are often very unequal, and sometimes much shorter than 

 the caudal segment. 



The above are some of the points in which the Anomobranchiates 

 exhibit their inferiority to the Macroura. 



Besides these peculiarities, there is a tendency to abnormal forms, 

 and to a separation of a true antennary segment, and sometimes both 

 antennary and ophthalmic segments, anterior to the thorax. In one 

 group (Luciferidae), an antennary segment forms a slender neck-like 

 prolongation anterior to the mouth. In another (Phyllosoma), it is 

 expanded into a broad leaf-like plate, and behind, it partially overlies 

 the part of the cephalothorax which follows it. In the Squilloids, the 

 ophthalmic and two antennary segments are distinctly marked. 



We have alluded to two series of forms among the Anomobran- 

 chiates, — the one Caridoid or shrimp-like, and the other more related 

 to Thalassina or Callianassa. In arranging the genera, these series 

 are of prominent importance. 



In the Caridoid series, there are two groups of nearly equal value ; 

 one the Myddoid, including Mysis and related genera, in which the 

 general form is shrimp-like, the body being subcylindrical, or more or 

 less compressed, the legs and their palpi, when present, being mainly 

 of the normal type, the palpus arising from the legs near the body ; 

 the other, the Amphionoid, having the body depressed or subfoliaceous, 

 and the thoracic legs long, with the palpus arising remote from the 

 body. 



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