PROCEEDINGS OF THE NATIONAL. MUSEUM. 



VOL. 64. 



dactylus mellitae all the spines are present and prominent (fig. 30). 

 The telson while characteristic in some families, is variable in the 

 Pinnotherids. Dissodactylus and Pinnotheres maculatus have the 

 bicornuate telson that is commonly found in the Brachyuran zoea 

 (figs. 28 and 37). In Pinnixa cTiaetopterana also the cornua are 

 elongated and cylindrical but the telson bears a median deltoid 

 process on its posterior margin (fig. 47). In all the other known 

 zoeas (except that of Pinnixa sayana (fig. 62) the median process is 

 present and the cornua are likewise reduced to short, thick processes 

 (figs. 17, 18, 50, and 51). 



KEY TO KNOWN ZOEAS. 



a.^ Telson bicornuate, without median process. 



b.^ Fifth abdominal segment expanded and produced posteriorly as lappets 



Pinnixa sayana. 

 6.2 Fifth abdominal segment not expanded. 



cA Prominent dorsal tubercle on first abdominal segment 



Dissodactylus mellitae. 

 C.2 No dorsal tubercle on first abdominal segment 



Pinnotheres maculatus. 



a? Telson bicornuate with median deltoid process Pinnixa chaetopterana. 



a.^ Telson not bicornuate, with three deltoid teeth posteriorly. 

 b.^ No spines on carapace or vestiges only. 



c.^ Pigment spot on second maxilliped Pinnotheres ostreum. 



c.^ No pigment on second maxilliped Pinnotheres holothuriae. 



b.^ Dorsal spine only absent Pinnotheres pisum. 



b.^ All spines present Pinnotheres veterum. 



PIGMENTATION. 



The pigmentation of the zoeas is constant for each species and is 

 helpful in classification. In all the known species, the color of the 

 pigment is light brown when fully expanded and black in contraction. 

 The following table gives the pigmentation of the known forms. The 

 notes on the pigmentation in the older descriptions probably are 

 incomplete. 



