386 CRUSTACEA 



FAMILY 1. CRANGONIDAE. 



Shrimps. Second antennae long, with a large 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. 



CBANGON Fabricius. Cephalothorax 

 somewhat depressed; rostrum short; first 

 antennae with 2 flagella: 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. 



C. boreas (Phipps). Three median dor- 



^second 'antenna?* 10 sa l 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 Paltzmonidae here described : 



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

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

 Ci First 2 pairs of periopods chelate. 



di Mandibular palp absent 1. PAL^EMONETES 



d, Mandibular palp present 2. PAL^EMON 



c 2 First pair of periopods not chelate 3. PANDALUS 



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

 the third segment. 



Cj Mandibular palp present 4. HIPPOLYTE 



c 2 Mandibular palp absent 5. VIBBIUS 



a, Right and left claws of the first pair of periopods of different size. .6. ALPHEUS 



1. PALS:MONETES 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. 



