Fishes of the Western North Atlantic 431 



Trunk moderately compressed, as usual in this genus, but somewhat stouter when 

 adult than in the diflana-zy gaena group, its dorsal profile moderately arched. No trace 

 of mid-dorsal ridge. Caudal peduncle about % as thick as high, the upper precaudal pit 

 strongly developed as a broadly triangular depression but no definite lower pit. Dermal 

 denticles close-spaced and overlapping regularly (laterally as well as longitudinally) but 

 with skin visible here and there, the blades but little arched longitudinally and not much 

 raised, very thin, about as broad as long, smooth toward base, but with 3 to 5 low rounded 

 ridges toward free margin in small specimen (perhaps 5 to 6 in large specimens), the mar- 

 ginal teeth rather short and broad, the median very little the longest; pedicels short and 

 thick; basal plates with 4 rather long rays. 



Head to origin of pectoral about Vs of length of trunk to origin of caudal or a little 

 less, its dorsal profile evenly convex posterior to eyes but concave forward to a rather thin 

 tip, hammer-shaped, the outer posterior margins slightly concave and nearly transverse 

 (sloping more strongly rearward in diplana and zygaena) ; width of head at eyes about 

 1.2 times its length to origin of pectoral in small specimens, the width of hammer rela- 

 tive to its length at oculo-narial prominences increasing from about 3 : i in very small speci- 

 mens to about 4:1 in medium-sized and large; anterior margin of head scalloped with a 

 depression opposite each nostril (not as deep as in the diflana-zy gaena group), a shallow 

 but unmistakable indentation in the midline, and a shallow sinuosity between these two; 

 the groove running from the nostril inward along anterior margin of head only very 

 faintly marked, but visible upon careful examination nearly halfway to the midline. Dis- 

 tance from anterior margin of eye to anterior corner of oculo-narial prominence about as 

 long as diameter of eye; a line connecting inner ends of nostrils passes anterior to front of 

 mouth by a distance nearly or quite twice as long as diameter of eye (not longer than 

 diameter of eye in the diplana-zy gaena group), one connecting centers of eyes passes 

 in front of mouth by a distance only about ^2 as long as diameter of eye in newborn speci- 

 mens but about I V2 times that long in larger (it passes close in front of mouth in diflana, 

 and a little posterior to it in zygaena) and one connecting outer posterior corners of 

 hammer passes a little posterior to corners of mouth in newborn specimens but anterior 

 to it in large by a distance at least V2 as long as diameter of eye (in adults of the 

 diplana-zy gaena group this line passes posterior to corners of mouth). Head in front of 

 mouth about Ys as long as to pectorals in small specimens but decreasing in relative length 

 with growth to only about Vs that long in large adults. Rostral cartilage with a median 

 oval or triangular hole, but wings of preorbital processes without inwardly directed points 

 on anterior margin (intermediate in this respect between diplana and zygaena). Mucous 

 pores in median belt on oral side of front of head covering a subtriangular area, much as in 

 zygaena. Eye a little broader than high, its horizontal diameter about Vs as long as head 

 in front of mouth in young but increasing so little in size with later growth as to be only 

 about Vs as long as head in front of mouth in large specimens (much smaller than in the 

 diplana-zy gaena group ).^* Gill openings extending ventrally, the ist to 4th nearly straight 



28. Diameter of eye i6 to 18 mm. in specimens of 700 to 72J mm. but only 25 mm. at a length of 1,735 to 1,745 

 mm., 26 mm. in a specimen of 2,370 mm., and 29 mm. in one of 3,155 mm. 



