386 CRUSTACEA 



Family 1. CRANGONIDAE. 



Sliriinps. Second antennae loni;, with a lari;e antennal scale; first pair 

 of periopods much stouter than the others and subchelate; second pair of 

 periopods small and chelate; mandibles slender, not bifid or expanded at 

 the tip and without a palp: marine; about 10 American genera. 



Crangon Fabricius. Cephalothorax 

 somewhat depressed; rostrum short; first 

 antennae with 2 flagellar 15 species, about 8 

 American. 



C. vulgaris Fabr. The edible shrimp 

 (Fig. 617). Length 5 cm.; color light, with 

 dark markings: Labrador to South Caro- 

 lina; Europe; Pacific coast; common at the 

 bottom of sandy bays, in shallow water, often 

 buried in the sand. 

 (L^Sis^''-i?T??\S?.^ C. boreas (Phipps). Three median dor- 



fca?e f 4rse%nd 'antenSl!""''^ sal spines on cephalothorax : Atlantic coast as 



far south as Cape Cod; North Pacific coast. 



C. franciscorum Stimpson. The California shrimp. Length 7 cm.; 



posterior margin of fifth abdominal segment with a spine on each side; 



movable finger of cheliped long and parallel with the hand: common at 



San Francisco. 



Family 2. PAL^MONIDAE. 



Prawns and shrimps. Second antennae long, with a large antennal 

 scale; first antennae with 3 flagella; third maxillipeds foot-like; mandibles 

 with a bifid tip ; rostrum long and usually serrate : mostly marine ; about 

 12 American genera. 



Key to the genera of Palcemonidae here described : 



ax Right and left claws of the first pair of periopods of the same size. 

 &i First pair of periopods shorter but not thicker than the second. 

 Ci First 2 pairs of periopods chelate. 



dx Mandibular palp absent 1. Pal^monetes 



dj Mandibular palp present 2. Pal^emon 



Cj First pair of periopods not chelate 3. Pandalus 



62 First pair of periopods thicker than the second ; abdomen bent down at 

 the third segment. 



Ci Mandibular palp present 4. Hippolyte 



C2 Mandibular palp absent T). ViRBlUS 



a2 Right and left claws of the first pair of periopods of different size. .6. Alpheus 



1. PALiEMONETES Heller. Mandibles without palp; first 2 pairs of 

 periopods chelate, the first pair being smaller than the second: about 6 

 species, 3 American, in salt, brackish, and fresh water. 



