-. CRUSTACEA. 



Sub-order II. Cormostomata (from *.^, trunk, and *»,«.). The 

 mouth having the form of a moveable trunk. 



Sub-order III. Merostomata (from W5 , thigh, and ™,*«). The 

 basal joints of the legs constituting the joints. 



Gnathostomata.— Among the Gnathostomata there are species with 

 an excessive or abnormal number of segments to the body, and 

 lamellar appendages below, corresponding to the segments. These 

 are naturally separated from the other species, which are essentially 

 normal in their characters, the variations in the normal species being 

 occasioned by obsolescence of parts, and not by increase. The former, 

 are very appropriately called Phyllopoda* by Latreille, in allusion to 

 the foliaceous character and great number of the appendages, while 

 the latter he designated LoPHTROPODA,f on account of the fact that 

 the feet are usually setigerous, being terminated or margined by long 

 hairs. 



The two groups include to some extent parallel forms, and admit of 

 parallel subdivisions. Cyclops or Sapphirina of the Lophyropoda is 

 analogous to Apus, among the Phyllopoda, and Cypris or Daphnia to 

 Limnadia. 



Moreover, these Phyllopodous species seem, in a certain degree, to be 

 recent representatives of ancient forms, the Trilobites, which were also 

 abnormal in the number of segments by a like multiplication. The 

 Gnathostomata are therefore naturally divided into these two groups, 

 the Phyllopoda and Lophyropoda. 



The Lophyropoda contain the natural groups or tribes Cyclopacea, 

 Daphniacea, and G/jpridacea, as usually laid down ; and the Phyllo- 

 poda, the Tribes Branddpodacea, Apodacea, and Limnadiacea. The 

 graduation of the Macroura into the maxillated Entomostraca is seen 

 through Mysis, Nebalia, and Branchipus, as observed by Milne 

 Edwards, all three having pedunculate eyes. 



The Cormostomata, or sucker-mouthed species, pertain to two widely 

 different types — one, the Cyclops type, as seen in Caligus (which has 

 closely the form of Sapphirina, one of the genera of the Cyclops group), 

 which group is named PoecUopoda by Latreille; and another, the 

 Arachnoid type, as in Nymphon, Pycnogonum, and the allied. The 

 former pass into the Lernea group ; the latter are like spiders in form, 



* From puAAav, leaf, and ^ev^faot. 



f From tepvpoq, having hairy or tail-like appendages, and novs, foot. 



