160 ALLAN HANCOCK PACIFIC EXPEDITIONS VOL. 9 



Scales cycloid, 50 in a lateral series. One scale row above arch of 

 lateral line, 8 rows below. Four scale rows between median portion of 

 lateral line and dorsal base at middle of body length, and 3 scale rows 

 between lateral line and anal base at the same point. Scales absent on 

 head and abdomen. Lateral line complete, arched anteriorly for 12 

 scales, thence descending abruptly to mid-line of sides, and continuing to 

 caudal base. Membrane of subopercle and interopercle expanded into a 

 thin membrane covering the throat and the pectoral and ventral bases. 

 Opercular fringe of 5 small fimbriae. Gill-rakers absent. Pseudo- 

 branchiae well developed. 



Color in alcohol light tan, with small, faint, brown markings along 

 bases of dorsal rays. Edges of a few lateral scales with small, dark 

 punctations. A small dark spot on mid-line of nape. Head same color 

 as body. Fins pale. 



Comparison. — Alyxodagnus sagitta differs from the only other known 

 species of this genus, M. opercularis, in having smaller scales, fewer 

 scales above and below the lateral line, longer pectoral fins, fewer fim- 

 briae in the opercular fringe, a more slender body, a longer head, and a 

 posteriorly inserted dorsal fin. 



Genus HETERISTIUS, new genus 



Genotype. — Heteristius jalisconis, new species. 



Body elongate, somewhat rounded anteriorly, becoming compressed 

 posteriorly. Greatest depth through pectoral base, the body tapering 

 gradually to caudal base. Head bluntly conical, not abruptly truncated 

 anteriorly. Mouth moderately oblique. Lips fringed with small fim- 

 briae, the fringe of the lower lip better developed than that of the upper. 

 Lower jaw slightly projecting, without fimbria or flap of skin at its 

 symphysis. Eyes superior, interorbital narrow. Narrow bands of small, 

 pointed teeth in the jaws; vomerine and palatine teeth absent. Pseudo- 

 branchiae present. 



Scales cycloid. Body entirely scaled, including abdomen, sides of 

 body behind pectoral base, and the area from above arch of lateral line to 

 upper edge of opercle. Head and fins naked. Lateral line present, 

 complete; arched anteriorly for about 19 scales, the length of the arch 

 about one-half that of median portion. 



Dorsal fin elongate, H-I-XIX or VHI, 19 or 20, its origin above 

 vertical limb of preopercle. First two spines close-set, united by deeply 

 incised membrane. Third spine short and blunt, free, placed in center 

 of wide interspace between the two anterior spines and the continuous 



