244 BULLETIN 180, UNITED STATES NATIONAL MUSEUM 



Table 27. — Measurements made on three species of Oplopomus, * expressed in 

 hundredths of the standard length 



Characters 



oplopomus 



vergens 



diacanthus 



Standard length 



Length of head 



Diameter of eye 



Length of maxillaries (mouth) . 



Greatest depth 



Length of snout 



Postorbital length of head 



Least width of preorbital 



Length of caudal peduncle 



Least depth of caudal peduncle 

 Tip of snout to or igin dorsal . . . 



Tip of snout to or igin anal 



Tip of snout to anus 



Longest ray spiny dorsal 



Longest ray soft dorsal 



Longest ray anal fin 



Longest ray pehic fin 



Longest ray pectoral fin 



Longest ray caudal fin 



Length first dorsal spine 



Length spine soft dorsal 



46.0 

 27.4 



8.7 

 10.6 

 22.2 



8.9 

 13.5 



4.3 

 19.8 

 11.5 

 33.2 

 58.0 

 51.0 

 19.5 

 18.5 

 20.4 

 27.2 

 23.9 

 25.0 

 10.0 

 11.3 



66.1 

 28.5 



8.7 

 10.0 

 22.8 



7.5 

 14.1 



3.7 

 21.6 

 12.3 

 34.8 

 58.0 

 53.5 

 16.4 

 17.8 

 16.4 

 22.4 

 21.9 

 23.9 

 10.0 



9.6 



34.3 

 24.8 



6.7 



7.6 

 16.3 



7.6 

 12.0 



3.8 

 22.5 



8.5 

 33.6 

 53.0 

 50.5 

 18.7 

 15.3 

 17.2 

 24.8 

 22.7 

 26.2 

 15.3 

 13.0 



1 0. oplopomus, U.S.N.M. No. 65971, Caroline Island; 0. vergens, U.S.N.M.No.93209, type from Cavite, 

 Philippine Islands; O. diacanthus, U.S.N.M. No. 116116, type from Canton Island. 



Remarks'. — This new species may be recognized by its slender 

 form, as the greatest depth is 16.3 percent and the least depth of 

 the caudal peduncle 8.5 percent of the standard length instead of 

 22.2 to 22.8 and 11.5 to 12.3 percent, respectively, in O. oplopomus 

 and 0. vergens. In the latter two species the first dorsal spine and 

 the first spine of the soft dorsal are shorter and stouter than in the 

 new species 10.0 and 10 percent and 11.3 and 9.6 percent, respectively, 

 instead of 15.3 and 13.1 percent. The following key also will aid 

 ill their separation: 



lo. Midline of nape scaled as far forward as scales on sides of nape or to eyes. 

 2a. Cheeks and opercles naked; preopercle without spines; greatest depth 



about 5.5 0. diacanthus, new species 



26. Cheeks and opercles fully scaled; preopercle with a pair of flatish spines; 



depth about 4.5 0. vergens Jordan and Scale 



16. Midline of nape mostly naked, except one or two scales in front of first 

 spine of dorsal fin ; scales on sides of nape extend only halfway to eyes ; 

 cheeks and opercles naked ; preopercle with two flatish spines ; depth 

 about 4.5 0. oplopomus (Valenciennes) 



Named diacanthus in reference to the two strong spines, one at the 

 front of each dorsal fin. 



Genus PERIOPHTHALMUS Bloch 



Periophthalmus Bloch, in Schneider, Systema ichthyologiae . . ., p. 63, 1801. 

 (Type, Periophthalmus papilio Bloch.) 



