CLASSIFICATION I05 



II. Subclass Malacostraca. — Number of segments constant; tho- 

 racic segments eight; abdominal seven or eight. 



1. Order Leptostracha. — With bivalved shell; abdomen with 

 eight segments. 



2. Order Thoracostraca. — With carapace covering the whole or 

 a part of the thorax ; abdominal segments seven. 



1. Suborder Schizopoda. — Thorax completely covered ; tho- 

 racic appendages biramous Mysis. 



2. Suborder Cumacea. — Last four or five thoracic segments 

 not covered by the carapace; eyes sessile or rudimentary. 



3. Suborder Stomatopoda. — Last three or four . thoracic seg- 

 ments not covered by the carapace ; eyes stalked ; five maxil- 

 lipeds Squilla. 



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

 appendages uniramous and three maxillipeds; otocysts in an- 

 tennules. 



1. Suborder Macrura. — Abdomen usually well developed. 



Crayfish, Lobster. 



2. Suborder Beachyura. — Abdomen small and concealed be- 

 neath cephalothorax more or less perfectly Crah. 



4. Order Arthrostraca. — No shell or carapace as a rule; with 

 seven (or six) walking limbs; eyes sessile. 



I. Suborder Isopoda. — No carapace; first thoracic segment 

 fused with hiead ; body flattened dorso-ventrally ; branchiae on 

 abdominal appendages Oniscus (sow-bug). 



3. Order Amphipoda. — No carapace; first thoracic segment 

 fused with head; body flattened laterally; branchiae on thor- 

 acic appendages Gammarus, 



