GILBERT: CERTAIN SCOPELIDS IN THE MUSEUM COLLECTION. 261 



possible to determine its relationships to MydopTium boops Richardson, 

 from the Pacific Ocean, a species which has usually been considered 

 identical with M. humholdti, but apparently without direct comparison. 

 In spite of the doubtful locality of the specimen in hand, it seems ad- 

 visable to place on record a more detailed account of its characters. It 

 differs from typical M. humholdti in having on each side 8 + 6, instead 

 of 8 + 8 anal photopliores, but the variation iu M. humholdti may weil 

 include this formula. It must be considered very doubtful, however, 

 whether any species will include all the variations which have been 

 attributed to M. humholdti. 



Measurements in hundredths of length without caudal (107 mm.) : Length 

 of head, 26.5; diameter of eye, 9 ; length of snout, 4.5; length of maxillary, 

 16.5; interorbital width, 8; depth of body, 21; least depth of tail, 7; 

 distance from snout to dorsal, 43 ; to adipose fin, 78 ; to ventrals, 45 ; to 

 anal, 62. 



Dorsal with 12 rays, including all rudiments ; anal, 20; pectoral, 14 ; ven- 

 tral with 8 fully developed rays and no evident rudiment. Lateral line, 41. 

 Gill-rakers, 6 + 1 + 16, on outer arch. 



The scales are mostly lost, but a few along the course of the lateral line 

 indicate that these are much deeper than the others. 



The ventrals are inserted under the front of the dorsal ; the anal fin is 

 entirely behind the dorsal ; the adipose fin is well in advance of the last anal 

 ray. The fins are all broken, so no indication can be given of the length of 

 the rays. 



The mouth and gill cavity are black, this color including the gill-arches and 

 the gill-rakers, but not the gill-filaments or the pseudobranchiae. 



Photophores. — A small dorsal antorbital organ, obscure in this specimen ; 

 a more evident lower antorbital, which seems to be persistent in adults. 



Suprapectoral distinctly nearer upper pectoral rays than lateral line. Upper 

 infrapectoral on base of lower pectoral rays and below; lower infrapectoral 

 somewhat below the line joining the upper with the first thoracic, its distance 

 from the former less than two-thirds its distance from the latter; the vertical 

 from the lower infrapectoral passes immediately before the second thoracic. 

 Upper pectoral interspace slightly longer than the lower. 



Thoracic photophores peculiar in having the first three pairs forming rather 

 widely diverging lines, the fourth pair less widely separated, about as in the 

 second pair, the fifth pair very widely divergent, opposite and partly external 

 to the outer ventral rays ; second and fourth interspaces equal, the third 

 shorter, two-thirds the first. 



Supraventrals verticallj^ above the fifth thoracic, a little nearer the latter 

 than the lateral line, distinctly above the line of the two lower supra-anals. 



First pair of ventral photophores nearer median line than are the inner 

 ventral rays, which are unusually far apart ; first three pairs of ventrals form- 



