ISOPODS OF NORTH AMERICA. 



549 



FIG. 594. ARGEIA PUGETTENSIS. FIRST INCUBA- 

 TOKY LAMELLA FROM SPECIMENS FOUND ON: , 

 NECTOCRANGON DENTATA FROM AFOGNAK BAY, 

 AFOGNAK ISLAND, x Hi. 6, NECTOCRANGON 



CRASSA FROM OFF CAPE NEWENHAM, ALASKA. 

 X9i. 



large number of these forms, the conclusion must be maintained that 

 these thoracic processes, well developed in the young female, of vary- 

 ing size and shape and sometimes so reduced as to be practically absent 

 in the adult female, have no specific value whatever. Giard and Bon- 

 nier have described their function as organs of fixation, which seems 

 a reasonable conclusion and one capable of explaining why so much 

 variation occurs in this respect 

 with each individual parasite. 



Body of adult female some- 

 what asymmetrical. Length, 14 

 mm. ; width, 11 mm. 



Head wider than long, 2 mm. : 

 3i mm., somewhat bilobed, with 

 a narrow frontal border, the an- 

 terior margin of which is slightly 

 arched or rounded. The frontal 

 border projects at the side in a 

 small angular lobe. Eyes absent. 

 The first pair of antenna? are composed of two articles a large basal 

 article and a small terminal one. The second pair are composed of 

 four articles. Both are small and not conspicuous on the dorsal side. 

 All seven segments of the thorax are distinct. Ovarian bosses are 

 present on the first four segments, where they occupy the sub-lateral 

 portion of the anterior part of the lateral margin. The epimera are 

 narrow plates lateral to the ovarian bosses on the anterior part of the 



segments. The epimera also 

 occupy the anterior part of the 

 lateral margin of the last three 

 segments, but the ovarian bosses 

 are not present on these seg- 

 ments. The posterior lobes on 

 all the segments are large and 

 irregular in outline, and more or 

 less produced in narrow, some- 

 what elongated processes, these 

 processes being usually more 

 developed on one side (the longer 

 side) than on the other. 

 All six segments of the abdomen are distinct. The lateral parts 

 are not developed in any of the segments. The sixth or terminal seg- 

 ment is small and posteriorly truncate. The uropoda are a pair of 

 simple, single-branched lamella?, somewhat elongated, with outlines 

 irregular, and attached to the sixth abdominal segment. There are 

 five pairs of double-branched pleopoda. The outer branches are elon- 



FIG. 595. ARGEIA PUGETTENSIS. a, DORSAL VIEW 



OF IMMATURE FEMALE. 6, VENTRAL VIEW OF 

 SAME. X 10. (FIRST POST-LARVAL STAGE.) 



