ISOPOD8 OF NORTH AMERICA. 373 



Measurements of a female 25 mm. long. 



mm. 



Width of head at the outer margin of eyes 4. 5 



W iilth of first thoracic segment 6. 5 



Width of second thoracic segment 8 



Width of third and fourth thoracic segments 9 



Width of fifth thoracic segment 8. 5 



Width of sixth thoracic segment 8 



Width of seventh thoracic segment 7. 5 



Length of abdomen 10. 5 



Length of antenna with flagellum 9 



Measurements of a male 28.5 mm. long. 



mm. 



Width of head 5.5 



Width of first thoracic segment 7. 5 



Width of second thoracic segment 8 



Width of third, fourth, fifth, and sixth thoracic segments 9 



Width of seventh thoracic segment 8. 5 



Length of abdomen 11 



Length of antenna with flagellum 10 



Measurements of a male 35 mm. long. 



mm. 



Width of head 6. 5 



Width of first thoracic segment _ 9 



Width of second thoracic segment 9. 5 



Width of third, fourth, fifth, and sixth thoracic segments 10. 5 



Width of seventh thoracic segment 10 



Length of abdomen 13 



Length of antenna with flagellum 10 



PENTIDOTEA WHITEI (Stimpson). 



Idotea whitei STIMPSON, Proc. Acad. Nat. Sci. Phila., 1864, p. 155. MIERS, Jour. 

 Linn. Soc. London, XVI, 1883, pp. 42-43. RICHARDSON, Proc. U. S. Nat. 

 Mus., XXI, 1899, pp. 846-847; Ann. Mag. Nat. Hist. (7), IV, 1899, p. 266; 

 American Naturalist, XXXIV, 1900, p. 227. 



Localities. Puget Sound; Monterey Bay, California. From Mytilus. 



Body narrow, elongate, with sides almost parallel; length equal to 

 a little over three times its greatest breadth, 11 mm. : 34 mm. Length 

 of abdomen a little more than one-third that of entire body, 12 

 mm. : 34 mm. 



Head wider than long, with frontal margin very slightly excavate; 

 posterior portion not wider than anterior portion. Eyes moderately 

 large, transversely ovate, compound, and placed close to the lateral mar- 

 gin, about halfway between the anterior and posterior margins. The 

 first pair of antennas have four articles; the basal article is twice as 

 broad as any of those following and a little longer; the next two articles 



