complete on both sides of two specimens, two have it complete on one side and 
interrupted on the other. 
side and 
the rest in so far as the specimens are fit for examination it is incomplete. 
THE AMERICAN TETRAGONOPTERINAE. 
interrupted on the other. 
In a number of specimens it is incomplete on one 
In five it is interrupted on both sides. 
Lateral line of Moenkhausia cotinho from Tumatumari. 
Seales with pores in italics. 
Left Right 
1, 30 30 
2, 30 31 
SG 2 Pip eal een bg 31 
Awe 23 +4-+ 4 
By Qe ae ee te eG, 20 eee 1 pe bes 
6, 16+4+2411 2+9+3 
Tie alee Set itt 20+10+2 
8, 8B+1+24+5 26 +1243 
Gig 83 ser ete tre hig 145 Fa eta esi as a) 
10, 21411 a1+1+2+8 
hieieee ee 12) 23 + 10 
1D, Gh) deo) See 18 + 14 
13, 16 + 16 16 + 16 
(Ap 17 RIS SU Say 
15, Dyas 124+2+24+15 
iGo ighe tl Ser eeae 13 + 19 
Wp, peo by ee aly 
1, FRETS 13 + 20 
19, 71 +20 12+ 18 
A eritical examination of the details given above shows a regular gradation 
from the completed lateral line of Moenkhausia at the top of the list to the 
incomplete line of Hemigrammus at the bottom. 
In specimens numbered 3 and 4 in which the line is complete on one side 
several pores failed of development, not at the end of the line but at some dis- 
tance from the end. In number 5 the line reaches the caudal on both sides but 
some pores are missing on both sides. In number 9 we find the same but the 
missing pores occur four scales further forward. In 6, 7, and 8 the line does 
not reach the caudal on one side and in all the rest it fails to reach the caudal 
on both sides. It becomes progressively shorter. Numbers 11, 12, 14, and 15 
show that the shortening may take place by the dropping, not of the last pore 
but of some pores in advance of it. 
In this series we see a regular progression without notable breaks from the 
condition which is considered to characterize one genus to the condition charac- 
