132 CALIFORNIA ACADEMY OF SCIENCES. 



The adult male figured by me measured as follows : 

 body, length 3. mm., width .8 mm.; head, length .62 

 mm., width .6 mm.; and the young as follows: body, 

 length 1.9 mm., width .53 mm.; head, length .5 mm., 

 width .5 mm. 



Lipeurus squalidus Nitzsch. (Plate x, figs. 6 and 7.) 



Gerinar's Mag. Entomol., 1818, vol. iii, p. 292. 



Pediculus anatis Fabricius, Systenia Eutornologia?, 1775, p. 345. 



Lipeurus squalidus Nitzsch. Gurlt, in Mag. f. d. ges. Tkierheilk., 1842, 

 vol. viii, p. 425; Denny, Monographia Anoplurorum Britannias, 

 1842, p. 176, pi. xiv, fig. 5; Grube, Middendorff's Eeise, 1859, 

 vol. ii, p. 486; Nitzsch (ed. Giebel), Zeitschr. f. ges. Naturwiss., 

 1866, vol. xxviii, p. 385; Giebel, Insecta Epizoa, 1874, p. 241, pi. 

 xvi, fig. 1; Piaget, Les Pediculines, 1880, p. 344, pi. xxx, fig. 5; 

 Taschenberg, Die Mallophagen, 1882, p. 162. 



This common species of the ducks has long been 

 known, and is widely distributed geographically and 

 zoologically. It has been taken on at least a dozen spe- 

 cies of ducks, and what have been called varieties of it on 

 still other species. The exact defining of squalidus has 

 not yet been accomplished. Piaget declares that four 

 resembling species (sordidus, depuratus, f rater and gra- 

 cilis) of Nitzsch and Giebel are simply squalidus ; Tasch- 

 enberg agrees with Piaget, and adds that Rudow's species, 

 rubromaculatus, punctulatus, cinercus and nyrocce, are, at 

 best, but varieties of squalidus. 



The evident truth is that the wide distribution of this 

 duck parasite has resulted in the noting of the many vari- 

 ations normal to any animal species whose peculiar habits 

 of life produce the comparative isolation of small groups 

 of individuals. The common occurrence of the parasite 

 and its hosts has resulted in its frequent capture, thus 

 affording opportunity for the examination of many indi- 

 viduals widely separated geographically. It seems to me, 

 under the circumstances, advisable to give a broad defini- 



