COPEPODS OF THE WOODS HOLE REGION 123 



two, about the same width throughout, and tapered only very 

 slightly. Total length, 6-7 mm. 



Remarks. — This species may be recognized by its large size, by the 

 length and slenderness of the caudal rami, and by the details of the 

 fifth legs in both sexes. The only previous record of the copepod on 

 this side of the Atlantic was the single female taken by Bigelow in 

 the Gulf of Maine and identified by the present author. The new 

 records here presented would indicate that princeps is more of a bot- 

 tom form than any other species of the genus. 



Genus PLEUROMAMMA Giesbrecht, 1898 



Body stouter and not so elongate as in Metridia; head either sep- 

 arated from, or fused with, the first segment, one of the two carrying 

 a conspicuous knob or luminous organ on the right or left side ; fourth 

 and fifth segments fused with rounded corners ; urosome 3-segmented 

 in female, 5-segmented in male ; rami of the first four pairs of legs 

 3-segmented ; proximal segment of second endopod invaginate at the 

 base on the inner side, with an overhanging spine; exopod of third 

 leg with a deep sinus on the outer margin of the first segment ; fifth 

 legs uniramose. 



Remarks. — Wheeler gave a diagnosis of both sexes of this genus, 

 but mentioned no species, and gave no record of any specimens. The 

 present material contains at least four species, so that the genus is 

 fairly common along our shores. The genus was originally called 

 PleuTOmma by Claus, and that name is used by Wheeler, but the name 

 had been preoccupied and so was changed by Giesbrecht. 



KEY TO THE SPECIES 



1. Forehead protruding in a sharp-pointed process xiphias (p. 124) 



Forehead smoothly rounded, without a process 2 



2. Proximal segment of first antenna with several small and 2 



large teeth upon its anterior margin abdominalis (p. 125) 



Proximal segment of first antenna without teeth, large or small 3 



3. End segment of fifth leg armed with 3 setae, inner one longer 



than entire leg robusta (p. 126) 



End segment of fifth leg armed with 3 short spines, about equal 

 in length and shorter than segment itself gracilis (p. 127) 



Urosome asymmetrical; luminous organ and fifth leg with 



shorter and broader end segment nearly always on left side 2 



Urosome symmetrical ; luminous organ and fifth leg with shorter 



and broader end segment nearly always on right side 3 



Forehead with a pointed process ; basal segment of first antenna 



without teeth on its anterior margin xiphias (p. 124) 



Forehead without a pointed process; basal segment of first 



antenna with small teeth on its anterior margin abdominalis (p. 125) 



