The Lateral Sensory System in the Muraenidae. 133 



The siipratemporal commissure agrees exactly with that of 

 Ophicthys excepting that the tliree primary tubes of the commissure, 

 a median one and one other on each side, are represented by simple 

 swellings of the canal without external openings. 



The preoperculo-mandibular canal agrees with that of Ophicthys 

 excepting that there are more mandibular pores, and that the dorsal 

 one of the three preopercular tubes is a blind one. 



Muraena helena. 



Muraena helena (figs. 9 — 12) differs markedly from Ophicthys and 

 Myrus in that the posterior nasal aperture lies on the top of the 

 head, about half-way between the eye and the mid-dorsal line, instead 

 of at the ventral edge of the upper lip. It lies on the outer end of 

 a short nasal tube, as does also the anterior aperture, the latter 

 aperture lying near the anterior end of the snout. 



The main infraorbital canal of the fish begins at a pore that lies 

 slightly ventral to the hind margin of the base of the anterior nasal 

 tube. From there the canal runs backward through a lachrymal and 

 two suborbital bones, and then turns upward and traverses two post- 

 orbitals and a small postfrontal. In this length of canal six primary 

 tubes are given off, one as the canal traverses the lachrymal, one at 

 the hind end of that bone, and the others^ between each two of the 

 succeeding bones as far as the postfrontal. The first three of these 

 tubes, that is the 2^^, 3^^, and 4:^^ tubes of the line, open on the 

 outer surface by a single pore; the next three tubes are blind. Bet- 

 ween the postfrontal and the skull there is no primary tube, the 

 main infraorbital canal there first anastomosing with the supraorbital 

 canal, and then turning backward and traversing a canal in the 

 skull. Up to the point where it here issues from the skull the 

 arrangement is thus similar to that in Ophicthys and Myrus. Posterior 

 to this point the arrangement differs from that in those two fishes in 

 that the canal of Muraeua, after it issues from the skull, first tra- 

 \'e]-ses a snmll and delicate tubular ossicle, near the middle point of 

 winch it anastomoses with the dorsal end of the preoperculo-mandibular 

 canal, and then traverses a second and similar ossicle, near the middle 



