516 U.S. NATIONAL MUSEUM BULLETIN 271 



LOWER LIP 



Normal gammaridean (fig. 2) . 



Inner lobes: weak (fig. 7ld), absent. 



Mandibular projection of outer lobes: pointed, obtuse, absent. 



Outer lobes: distally notched; medially excavate (Ampithoidae, figs. 50c,d). 



Special shapes: Pleustidae (fig. 37a), Trischizostoma (fig. \2bv). 



MAXILLA 1 



Inner plate: 



Size: absent (very rare), small (fig. 127/), medium (fig. 127e), as large (broad 

 and bulkjO as outer plate (rare). 



Setation: terminal, medial, or both. 



Number of setae: 1, 2, 3, 4-6, 6-12. 



Structure of setae: normal; sickle-shaped or strongly constricted. 

 Outer plate: 



Number of spines: 1-4, 5-6, 7-8, 9-11 + . 



Shape of spines: normally slender, extremely stout, some bifid, some serrate, 

 in two distinct groups by position or structure. 

 Palp: 



Number of articles: 0, 1, 2. 



Normal structure: article 1 short, article 2 long. 



Article 1 long, article 2 short. 



Modifications: strongly bent (geniculate), foliaceous, bearing scales (examples: 

 Stilipedidae, Hyperiopsidae). 



MAXILLA 2 



Normal gammaridean (fig. 127o). 



Abnormally small, plates partially coalesced, setae very sparse. 



Breadth of lobes: subequal, inner broader, outer broader. 



Axial divergence of lobes (fig. 127 j). 



Extension of outer plate on basal article (fig. 161a). 



Specialized spines (rare). 



Extent of medial setation on inner plate: strong, sparse, absent. 



MAXILLIPED 



Inner lobes (proximal) : 



Size: vestigial (fig. 128e), normal (fig. 128a). 



Abnormal shape: foliaceous (rare), styliform (note: inner lobes often appear 

 styliform if not fully depressed by cover slip). 

 Older lobes: 



Size relative to inner: usually larger, vestigial (fig. 114d), foliaceous (rare). 



Spination: absent, medial, distal. 

 Palp: 



Extension in relation to outer plate: shorter, equal, longer. 



Number of articles: 0, 2, 3, 4. 



Medial or terminal extensions of articles, e.g., lobes, cusps: articles 1, 2, 3. 



Elongation of articles 1, 2, 3. 



Terminal palp article (usually 4): claw-like (normal); barrel-shaped; vestigial; 

 bearing distal nail, spine, or setae. 



