MARINE GAMMARIDEAN AMPHIPODA 457 



downtnrned rostrum; pereonites 1-4 often very short; gnathopods 

 feeble, slender, scarcely siibchelate; eyes when present dorsally 

 confluent. 



Relationship. — Synopiids differ from the basic gammaridean 

 mainly by the massive head with large rostrum, poorly developed 

 mandibular palp in most genera, feeble gnathopods, and elongated 

 telson. From the Eusiridae they differ by the combination of the 

 same characters, except for the elongate telson. They are similar to 

 the Oedicerotidae in head, eyes, and general appearance, but all 

 Oedicerotidae have a vestigial or no accessory flagellum, usually 

 powerful gnathopods and short, uncleft telson. 



Synopiidae differ from Pardaliscidae by the possession of a man- 

 dibular molar but often appear similar in other ways, except that 

 the coxae of Pardaliscidae are always very short. 



The Vitjazianidae differ from Synopiidae by the small, poorly 

 rostrate head. 



The Argissidae have a normal gammaridean head, practically no 

 rostrum, and a unique pattern in the shapes of coxae 1-4. 



Astyridae resemble Synopiidae closely and differ from them in 

 the occurrence of just one or two articles in the accessory flagellum, 

 the setose, laminate, and not triturative mandibular molar. All 

 synopiids, except Bruzeliopsis, have a reduced palp article 3 on the 

 mandible, whereas astyrids have an elongated article 3. All Astyridae 

 have short telsons and widely spaced outer lobes on the lower lip. 



A revision of Synopiidae is presented herein and where generic 

 composition has been changed, the species have been listed. 



Key to the Genera of Synopiidae 



Mandibular molar very large and smooth (minutely setulose or fuzzy oc- 

 casionally), completely dominating mandible, body of mandible extremely 

 bvilky, subglobular, dwarfing palp (fig. 166d) 2 



Mandible as in first triplet but palp absent Jeddo 



Mandibular molar of medium size, occasionally smooth and minutely fuzzy 

 but usually triturative, body of mandible usually stout but not extra- 

 ordinarily bulky or subglobular, palp relatively strong (fig. 166e) ... 5 



Coxa 3 strongly expanded anteroposteriorly and much larger than coxa 4 

 (fig. 166a) (more than twice as much surface area), coxa 3 with strong 

 posterodorsal excavation dorsal to expansion, article 1 of antenna 1 very 

 elongate and bearing long subconical distal process, articles 2 and 3 short 

 and subequal in length, coxa 4 very small and shaped like a comma (fig. 

 166a) Bruzeliopsis 



Coxae 3 and 4 subequal in size and length, coxa 3 never with more than 1.5 

 times as much surface area as 4, coxa 3 weakly expanded or not expanded 

 distally, lacking distinct posterodorsal excavation, coxa 4 adze-shaped or 

 quadrate, its posteroventral lobe or midposterior cusp distinctly directed 



