THE LEPTOCEPHALUS OF THE AMERICAN EEL. 
83 
Several characters used in the following key have proved of but transient value. 
The approximation or separation of the nares we have found in one case to depend 
on the age of the specimen. The presence or absence of the pectorals we have also 
found to depend at times on the age of the specimen. Whether these two characters 
are ever of permanent value we are unable to say. 
Key to the species of Leptocephali described in the present paper . 
a. A series of three or four large conspicuous black spots on each side. Segments 114 to 116. Other charac- 
ters differing greatly with age diplychus 
act. Sides without large conspicuous black spots. 
6. Pectorals none; nostrils remote. 
c. Head depressed between the eyes; 96 abdominal, 40 caudal segments giltii 
cc. Head swollen between the eyes; a series of black dots along back and belly. 
d. Anus near middle of length; eye large, 1.6 in snout; gradually tapering from snout to anus, 
thence decreasing gradually to the tail; no pigment about 
head, except in gular region; segments 70 + 71 strommani 
dd. Anus much nearer tip of caudal than snout; eye small, 2.5 in snout; rapidly widening from nape 
to about the twenty-fifth segment, then of nearly uni- 
form width to anus at ninety-eighth segment, thence 
tapering to tip of tail; pigment dots on top of head; seg- 
ments 98 + 35 .lotus 
bb. Pectoral fins present. 
e. Caudal suddenly contracted; head conical; eye small, 2.66 in snout; nostrils remote; seg- 
ments 66 + 80 mucronat.us 
ee. Caudal not contracted, the vertical fins continuous with it. 
/. Nostrils remote. 
g. Snout obtuse, lower jaw the shorter. 
li. No color along the middle of the sides. Segments about 60 + 60 rex 
hh. A series of spots along the middle of the side; another along the ventral margin; 
segments 54 + 88 (see also n) morrisii 
gg. Snout pointed, jaws equal. 
i. Body short, elliptical; no pigment; tongue free in front; segments 68 + 40 grassii 
ii. Body elongate, band-shaped. 
j. Eye 1.5 in snout; nostrils above the level of the middle of the eye; a series 
of rounded spots along the middle of the sides, one to 
each 2 to 3 segments; segments 72 + 83 discus 
jj. Eye 1.5 in snout; nostrils on level with middle of eye; tongue not free in 
front; a series of elongate spots along the middle of the 
sides, one to each segment; segments about 160 humilis 
ff. Nostrils approximated; body elongate, nearly band-shaped; a series of spots below the mid- 
dle of the sides. 
k. Vent near the posterior end of the body; color along sides consisting 
of a series of round chromatophores on the somites amphioxus 
kk. Vent near the middle of the body. 
1. A series of spots in the tail just beneath the notochord; segments 
127 to 130 caudomaculatus 
. K. No spots in the tail. 
vi. A series of chromatophores along the base of the dorsal rays; 
segments about 159 to 162 humilis 
mm. No chromatophores along the base of the dorsal rays. 
n. Segments 142 morrisii 
nn. Segments 180 gilberti 
All drawings illustrating this paper were prepared by Mr. Clarence Hamilton 
Kennedy. 
