528 



BULLETIN 100, UNITED STATES NATIONAL MUSEUM. 



to the following conclusion : there are in the Philippine Islands, and 

 in the adjacent regions to the northward and southward , three geo- 

 graphical subspecies which apparently intergrade in the tioo regions 

 where their ranges meet. The typical striatissimus, originally de- 

 scribed from Japan, ranges southward to China, Formosa, and the 

 east coast of Luzon. It intergrades off the northwest coast of Luzon 

 with the subspecies torvus, which inhabits the Sulu Sea and the China 

 Sea off southern Luzon. The form torvus then intergrades, along the 

 Tawi Tawi Archipelago, with the third subspecies, aeger, which in- 

 habits the East Indian Islands south of the Philippines. 



The diagnostic characters, in so far as we have been able to analyze 

 them, seem to be but three or four in number : 



1. The ventral rays in striatissimus and aeger are 8 in number, 

 while in torvus, which occupies a region between the other two forms, 

 there are 7. 



2. The orbit is nearly circular and very large in striatissimus, but 

 smaller and more obliquely elongate in torvus and aeger. 



3. The barbel is usually longer than the pupil in the southern 

 form aeger, about as long as the pupil in the typical striatissimus 

 and usually shorter than the pupil in the central subspecies, torvus. 



4. The color may average darkest in torvus, but the character is 

 not constant and is not very valuable in distinguishing the sub- 

 species. 



It will be noted that the intergrades between striatissimus and 

 torvus have the eight ventral rays of the former, but usually have 

 the small and less regular orbit and the short barbel of torvus. The 

 intergrades between torvus and aeger likewise usually have eight 

 ventral rays, and have the small irregular orbit as in both torvus 

 and aeger. It follows from these facts that the tw T o sets of inter- 

 grades are difficult to distinguish from one another, although the 

 three typical forms may readily be separated. The chief average 

 difference between the intergrades seems to be in the length of the 

 barbel, which averages greater in the specimens from the Tawi Tawi 

 group than in those from off northwest Luzon. 



Tables showing the diagnostic characters of the subspecies of Hymenocephalus 

 striatissimus and of the intergrades between these subspecies. 



VENTRAL RAYS. 1 



Species. 



striatissimus -. 

 Intergrades . . . 



torvus 



Intergrades . . 

 aeger 



2 



302 



30 



2 



111 

 125 



1 Number of fins, not specimens, are ^numerated; the number is often not the same on the two sides o 

 the same fish. 

 ?.bipane=e material included; the types, not here listed, also have 8 ventral rays. 



