424 INTERTBBRATE MORPHOLOGY. 



2. Subclass Thoracostraca. — With carapace covering the whole or a 



part of the thorax ; abdominal segments seven. 



1. OvAev ScMzopoda. — Thorax completely covered ; thoracic append- 



ages biramous. Mysis, Euphausia, Siriella. 



2. Order Cumacea. — Last four or five thoracic segments not covered 



by the carapace ; eyes sessile or rudimentary. Diastylis, 

 Campylaspis. 



3. Order iStomatopoda. — Last three or four thoracic segments not 



covered by the carapace ; eyes stalked ; five maxiUipeds. 

 Squilla, Lysiosquilla, Qonodactylus. 



4. Order Decapoda. — Thorax completely covered ; five posterior 



appendages uniramous and three maxillipeds ; otocysts in 

 antennules. 



1. Suborder Macrura. — Abdomen usually well developed. Ser- 

 gestes, Lucifer, Penoeus, Palcernonetes, Alpheus, Cambarus, 

 Homarus, Eupagurus, Birgus, Hippa. 



2. ^abavAev Brachyura. — Abdomen small and concealed beneath 

 cephalothorax more or less perfectly. Poroellana, Lihinia, 

 Callinectes, Platyonychus, Cancer, Pinnotheres, Ocypoda, 

 Qelasimus, Qecarcinus. 



3. Subclass Arthrostraca. — No shell or carapace as a rule ; with seven 



(or six) walking-limbs ; eyes sessile. 



1. Order Anisopoda, — Carapace slightly developed : first two tho- 

 racic segments fused with head ; branchiae on anterior maxiUse. 

 A seudes, Tanais, Anthura. 



3. Order Isopoda.—'So carapace ; first thoracic segment fused with 

 head ; body flattened dorso-ventrally ; branchiae on abdomi- 

 nal appendages. Asellus, Oniscus, Porcellio, Armadillid- 

 ium, Idotea, Sphmroma (free) ; Cymothoa, Mga, Bopyrus, 

 Entoniscns (parasitic). 



3. Order AmpMpoda. — No carapace, first thoracic segment fused 

 with head ; body fiattened laterally ; branchise on thoracic 

 appendages. Cfammarus, Orchestia, Gorophium, Cyatnus, 

 Caprella. 



LITERATURE. 



H. Milne-Edwards. Histovre Naturelle des Orustaces. Paris, 1834-1840. 



F. Mttller. Fiir Darwin. Leipzig, 1864. 



H. Gerstaeoker. Arthropoda. Bronn's Klassen und Ordnungen des Thier- 



reichs, Bd. v. Abth. 1. 1866- (not j'et completed). 

 C. Claus. Untersuehungen zur Erforschung der genealogisclien Cfrundlage des 



Grustaceen-Systems. Wien, 1876. 

 C. Grotben. Die Antennendrilse der Crustaceen. Arbelten a. d. Zoolog. Inst. 



Wien, m, 1880. 



