LAMPERN. 
1191 
not uncommon, are bicuspid instead of tricuspid — there 
not only appear anterior suctorial teeth (ist, above in 
the figure), in almost the same arrangement as those of 
the Sea Lamprey and with lozenged frames, but the 
male also possesses, on the posterior part of the disk, 
a curved though irregular row of teeth (ist, below in 
the figure). The specific character in the anterior dental 
plate of the mouth (at) we have pointed out above. The 
posterior dental plate (pt) is of the same form as in the 
preceding species; but its two outermost cusps are larg- 
er than the others and oftenest bifid (bicuspid). The 
number of cusps between them is as a rule five, excep- 
tionally (fig. 353) four, so that the total number of cusps 
varies between 7 and 9. The lateral dental plates of 
the mouth (alt, mlt , and pit) are similar to those of the 
preceding species, but lie farther apart, and the middle 
pair on each side (mlt) are, as we have mentioned, 
usually tricuspid. The anterior linguodental plate ( aln ) 
is crescent-shaped, with the median cusp on the uni- 
formly curved margin largest, and with 5 or 6 small 
cusps on the lateral parts. The posterior linguodental 
plates lie, when at rest, deep in a groove between the 
tumid lateral halves of the tongue", and are only slightly 
curved but otherwise of the same form as in the pre- 
ceding species. Their 10 or 12 retral teeth are very small. 
The orifice of the nasal duct undergoes almost the 
same alterations as in the preceding species. In the 
Pride it is pear-shaped, anteriorly pointed, with the 
dermal margin more elevated and expanded behind. In 
the Lampern it is more uniformly round, with the mar- 
gin more or less elevated. In consequence of the some- 
what shorter snout, the distance between this orifice and 
the tip of the former is also less than in the Sea Lam- 
prey. In the Pride this distance is rather less than 2 /s 
(about 37 7g %)■> in the Lampern rather less than 3 / 5 
(about 53 — 59 % h ), of the length of the head to the first 
gill-opening. The series of gill-openings is somewhat 
longer than in the preceding species, varying, however, 
between about 9 1 ,/ 2 and 11 Vs % of the length of the 
body; and the several gill-openings may be closed from 
the anterior margin by a continuous, even flap of skin. 
In the Lampern too their posterior margin is verruculose. 
In the form and position of the fins we can indeed 
distinguish between two varieties of Lampern, but only 
with far from reliable characters; and the variability in 
these relations is such that we cannot even state a per- 
fectly trustworthy distinction between the Lampern and 
the Sea Lamprey. The rule, however, is that the limit 
between the caudal fin and the second dorsal is less 
distinct in the Lampern; and as the two dorsal fins are 
sometimes contiguous, and a fin-like, though rayless, 
est 
Fig. 353. Oral disk of a male Lampern ( Petrornyzon fluviatilis , var.), 
3 1 1 / 2 cm. long from Archangel, X 2. Signification of the letters 
explained in the preceding figure. 
dermal ridge is usually perceptible between the caudal 
fin and the anus, the Lampern may be regarded as a 
lower form, with more distinct vestiges of the larval 
condition. As regards the difference between the two 
assumed varieties of Lampern, it has been asserted, first 
and foremost, that the exclusively fresh-water form 
Petrornyzon brancliialis or Planeri in general has higher 
and closely contiguous dorsal fins. According to K ro- 
ver the following relations hold good: 
o o 
Petrornyzon 
Petrornyzon 
Planeri. 
fluviatilis . 
Length of the body expressed in millimetres - - 
144—261 
333—392 
Greatest height of the first dorsal fin in % of the total length of the head and branchial region 
11.1—14.8 
o> 
1 
00 
to 
,, ,, „ ,. ,. ,, ,, ,, „ „ „ distance between the first dorsal and the tip of the snout 
5.i — 6.6 
3.2 — 3.3 
,, ., ,, second „ „ „ „ „ total length of the head and branchial region 
20—32.4 
17.6—18.2 
„ ,. ,. ,, „ ,, „ „ ,, distance between the first dorsal and the tip of the snout 
9.2—14.6 
6.9 — 7.7 
a Our figure (PI. LIII, fig. 2) of the oral disk, as it appeared through the glass wall of an aquarium, where the Lampern had at- 
tached itself, shows in the middle these lateral halves, separated by a V-shaped groove under the anterior dental plate of the mouth. Under 
them the anterior linguodental plate, which is also white, may be seen; hut the dental cusps are too minute to be visible in the figure. 
h In the preceding species about 63 — 68 %. 
Scandinavian Fishes. 
150 
