46 U.S. NATIONAl, MUSEUM BULLETIN 271 



flagella; then a group with normal accessory flagella but with various 

 combinations of degraded molars, characteristic rostra, coxae, and 

 pereopods, until finally the Gammaridae are reached. 



After the Gammaridae is the group of isaeid-like families, most of 

 which form tubes, have spinning glands in the pereopods, bear short, 

 uncleft fleshy telsons, posteriorly unexcavate coxa 4, and normal 

 mouthparts but which often have increasingly complex or reduced 

 uropods difficvdt to separate from the network of families anterior to 

 the Gammaridae. The identifier must keep them in mind. Some 

 genera of the isaeid-like families are very difficult to recognize and 

 all of these family keys and diagnoses should be examined when 

 identifying presumed Corophiidae, Aoridae, Isaeidae, Ischyroceridae, 

 Ampithoidae, and Podoceridae. Perhaps it is wise to become familiar 

 with known variations in characters of these families for it is often 

 difficult to recognize spinning glands in pereopods (and some genera 

 of isaeid-like families lack them). Shallow-water isaeids are usually 

 strongly pigmented in browns and purples but this is not a reliable 

 character, because other families occasionally have strongly pigmented 

 species. 



Example 1: Perhaps the observer determines from the completed 

 checklist (Appendix II), that the characters of the box Liljeborgiidae 

 (fig. 41) fit the specimen being identified. All characters match those 

 of the basic gammaridean except for the mandibular molar, which is 

 nontriturative ; the accessory flagellum is multiarticulate, the mandible 

 has a 3-articulate palp, the maxiUae are normal, maxillipeds have well 

 developed lobes and 4-articulate palps, gnathopod 1 is of normal or 

 enlarged size and is subchelate, gnathopod 2 is enlarged and sub- 

 chelate, all pleonites are free, pereopods are generalized, uropod 3 is 

 large and biramous, and the telson cleft. The caption lists related 

 families or those families with which Liljeborgiidae might be confused 

 and their boxes should be examined for special combinations of char- 

 acters not shared with the specimen at hand. For instance, the 

 Liljeborgiidae caption lists Gammaridae and Eusiridae as congruent 

 families, but the box of Eusiridae (fig. 39) indicates (1) by the absence 

 of a drawing of the mandible that it is either hke the basic gam- 

 maridean and therefore has a triturative molar, or is of variable char- 

 acter; and (2) that the accessory flagellum is 0-2 articulate. If the 

 specimen being identified has an accessory flagellum of 3-plus articles 

 then it is not a eusirid; if it has a 2-articulate accessory flagellum and 

 triturative molar then it is not a liljeboriid; if it has a 2-articulate 

 accessory flagellum and a nontriturative molar it may be either a 

 eusirid or liljeborgiid and the reader would turn to the descriptions of 

 those families (p. 213 and p. 291) and compare them with the speci- 

 men. He would read the sections on Kelationships to discover that a 



