No. 3.] LATERAL LINE OF AMIA. 487 
cross-commissure. This median system ts a double one (Cut 3, 
g:), and there are on each side of the head three other similar 
systems, making seven in all. One is formed by the fusion of 
systems 15 infra-orbital and 7 supra-orbital; a second one by 
the fusion of 17 infra-orbital and 17 operculo-mandibular, and 
the third by the union of the two portions of the operculo- 
mandibular canal. This last system, being formed in the line 
of its canal, is called No. 11 of that line. The other two 
being formed at the points of anastomosis of two different 
lines, have each been given a double number which indicates 
the position of the system on each of the lines to which it 
belongs. Counting it this way, there are three peripheral 
systems along the supratemporal cross-commissure, eight along 
the supra-orbital line, seventeen along the operculo-mandibular, 
and twenty-one along the infra-orbital; but as a median double 
system has disappeared at the point where the two infra-orbital 
lines unite on the top of the snout, there are properly twenty- 
two systems along this line, seventeen of them up to the point 
where it is joined by the operculo-mandibular. 
Surface Pores. 
The peripheral canal systems are represented on the surface 
of the head by more or less distinct groups of pores. The 
number of pores in some of these groups can be easily de- 
termined by surface examination; but in many cases several 
groups are so run together that only the general position of 
each group and the total number of pores in the series can be 
ascertained. 
For the following description three specimens were used : 
two males, one 17 in. and the other 20} in. in length, and a 
female 27 in. long. The number of pores given in the different 
groups, unless otherwise specified, applies only to the left side 
of the head, a comparison being made in every case with the 
number of openings in the skeleton. The arrangement of the 
surface pores in the larger male is shown in Figs. 20, 21, and 
22, Pie XVI. 
1. Lnfra-orbital Line. — The first group of the infra-orbital 
line, group 2, lies near the base of the nasal tube, a little in 
front of and median to it. It has usually one or two pores 
