MARINE GAMMARIDEAN AMPHIPODA 267 



and 2 equal in size. One must also examine Neomegamphopus , now 

 assigned to Aoridae, as an intermediary between Isaeidae and Aoridae. 

 All Isaeidae with male gnathopod 1 having secondary sexual modi- 

 fications have been removed to the Aoridae. 



The Ischyroceridae have the rami of uropod 3 shorter than the 

 elongate peduncle and usually have one or more distinct hooks or an 

 uncinate condition on the outer ramus. 



The Ampithoidae have an even more stunted third uropod than do 

 isaeids, the outer ramus of which usually bears hooks; the ampithoid 

 lower lip has notched or medially excavate outer lobes. 



The Corophiidae have a depressed urosome although this is not 

 clearly distinct in some intergrading genera; all but a few corophiids 

 have aberrant third uropods lacking one ramus, although a few 

 Isaeidae also demonstrate this; some corophiids and isaeids are 

 not clearly distinct and the taxonomist must use both family keys 

 for doubtful genera. 



Gamacho and Parunciola in the Corophiidae and Aorcho, now 

 assigned to the Aoridae, show the difficulty in clearly distinguishing 

 among isaeids, aorids, and corophiids. These genera, with their 

 moderately or fully depressed urosomes, equal-sized gnathopods, 

 biramous third uropod [or uniramous third uropod with long ramus], 

 and circular or quadrate telsons, lacking hooks, could be assigned 

 to any of the three families. 



The loss of one ramus of uropod 3 in five isaeid genera confounds 

 technical distinction of Isaeidae from several other, distantly re- 

 lated families having uncleft telsons. Cressidae, Stenothoidae, and 

 Thaumatelsonidae are distinguished from isaeids by their small 

 first coxae. Eophliantidae have cylindrical bodies and Phliantidae, 

 Talitroidea, and Dogielinotidae lack mandibular palps. Sebidae 

 have chelate gnathopods and obsolescent mandibular molars and 

 Pagetinidae have evanescent mandibular molars and poorly developed 

 outer plates of the maxillipeds. 



Nomenclatural Changes in Isaeidae 



Amphideutopus J. L. Barnard (1959a) is removed to the Aoridae. 

 Audulla Chevreux (1901a) is assigned in the Isaeidae as subgenus 



to Gammaropsis. 

 Bathyphotis Stephensen (1944b) is removed to the Ischyroceridae. 

 Bonnierella Chevreux (1900) is removed to the Ischyroceridae but 



is also assigned in the Isaeidae to Megamphopus. 

 Eurystheus dentatus Holmes (1908) is removed to Protomedeia 



(Cheirimedeia). 

 Leptocheirus Zaddach (1844) is removed to the Aoridae. 



285-135 O - 69 - 18 



