1. Posterior margin of telson with 2 pairs spines. Pleurobranch on third maxilliped. Rostrum always with teeth.............. 2

– Posterior margin of telson with 3 pairs spines. No pleurobranch on third maxilliped. Rostrum with or without teeth........ 4

2. Carpus of pereopod 2 distinctly shorter than chela. San Diego, California south........................ Palaemon ritteri

– Carpus of pereopod 2 longer than chela. San Francisco Bay south............................................... 3

3. Rostrum with subapical tooth, mandible with palp. Total length can exceed 25 mm............... Palaemon macrodactylus

– Rostrum without subapical tooth, mandible without palp. Total length reaching 25 mm.............. Palaemonetes hiltoni

4. Rostrum without dorsal teeth............................................................................ 5

– Rostrum with dorsal teeth............................................................................... 6

5. Body stout, major chelipeds heavy, lobster-like. Symbiotic with ascidians..................... Ascidonia californiensis

– Body, major chelipeds slender. Not symbiotic with ascidians................................ Pseudocoutierea elegans

6. Rostrum arched over eye, carapace without supraorbital teeth................................ Periclimenesinfraspinis

– Rostrum not arched over eye, carapace with supraorbital teeth................................. Palaemonella holmesi