440 



BULLETIN 58, UN-ITED STATES NATIONAL MUSEUIM. 



There are several well-marked color varieties which have received 

 varietal names. Their exact status has not been made clear, but 

 while it is true that they do not seem to represent local races, there is 

 nevertheless a certain regularity in their distribution. Thus the ordi- 

 nary black-backed form seems to be almost exclusive in the Pacific 

 Ocean; spotted individuals, such as the one figured in Fauna Japonica, 

 l)late VIII (from the west coast of Borneo) appear to occur mostly in the 

 Indian Ocean. All the specimens from eastern China, Formosa, Riu 

 Kiu, and Japan, so far as the records show, are of the black-})acked 

 form. 



Description (figs. 355-^57).— Adult female; U.S.N.M. No. 17518; 

 harbor of Nagasaki, Kiusiu; December 15, 1883; P. L. Jouy, col- 

 lector. Head very depressed ; snout elongate, the distance from eye to 

 tip of snout equaling the width of head at ])osteri()r end of supra- 



355 357 



Figs. 355-357.— Hydrus platurus. IJ x nat. size. 355, top of head; 35ti, side of head; 357, 



UNDERSIDE OF HEAD. No. 8, Scl. COLL. TOKYO. 



oculars; rostral nearly as high as broad, w^ell visible from above; nasals 

 not much longer than prefrontals, the suture between the former about 

 twice as long as between the latter; frontal much longer than its dis- 

 tance from tip of snout and nearly as long as parietals, much wider 

 than supraoculars; parietals long, with irregular outlines, a small inter- 

 calated shield in the suture between them; no loreal; a long preocular, 

 pointed anteriorly; tw^o suboculars; two postoculars; three anterior 

 temporals; ten supralabials, second largest, in contact with pre- 

 frontals, fourth to tenth small and low, none entering eye; no differ- 

 entiated chin-shields; 61 scale rows around middle of body, the scales 

 hexagonal, juxtaposed, smooth; no difi'erentiated ventrals or sub- 

 caudals; two slightly enlarged scales, one at each side in front of vent; 

 terminal scale on tail somewhat enlarged. Color (in alcohol) on back 

 dark seal-brown, sides and underparts abruptly clay-colored, the 



