PALAZZOSPONDYLUS. 527 
Lampreys are distributed in the rivers and seas of north and south 
temperate regions. They are often used as food. Besides Petromyzon 
there are several related genera, e.g. Mordacia and Geotria, from the 
coasts of Chili and Australia, and /chthyomyzon, from the west coast 
of N. America. Certain structures called ‘‘conodonts,” from very 
ancient (Silurian) strata, have been interpreted as teeth of lampreys 
or hags. 
Palzospondylus gunni.— Under 
this title Dr. Traquair has de- 
scribed a very remarkable fossil 
form from the Old Red Sandstone 
of Caithness. He'speaks of it 
as a “strange relic of early verte- 
brate life.” 
It is a dainty little creature, 
somewhat tadpole-like at first 
sight, usually under an inch in 
length. The following characters 
point strongly to its affinities with 
Cyclostomata :— 
(1) ‘The skull is apparently formed 
of calcified cartilage, and devoid of 
discrete ossifications.” An anterior part 
is comparable:to the trabecular and 
palatal region of a lamprey’s skull; 
a posterior part is comparable to the 
parachordal region and auditory cap- 
sules. 
(2) **There is a median opening or 
ring, surrounded with cirri, and presum- 
ably nasal, in the front of the head” 
(Fig. 278, ‘n.)s 
(3) ‘*There are neither jaws nor 
limbs.” 
(4) “The rays which support the 
caudal fin expansion, apparently spring- 
ing from the neural and hzemal arches, 
are dichotomised (at least the neural 
ones), as are the corresponding rods in 
the lamprey.” 
Just behind the head lie two small 
oblong plates (Fig. 278, x.), closely 
apposed to the commencement of the 
vertebral column, one on each side. 
The notochordal sheath is calcified in 
the form of ring-shaped or hollow verte- 
Fic.278.—Restored skeleton 
of Palaospondylus gunni. 
—After Traquair. 
d.c., Cirti of dorsal margin 3 Zc., 
long lateral cirri; v.c., cirri of 
ventral margin ; 2., nasal ring ; 
“.p., anterior ‘trabeculo- -palatine 
part of cranium; 4., anterior 
depression or fenestra ; 3 C-, pos- 
terior depression or fenestra ; 3 
@., lobe divided off from anterior 
part; #.@., posterior or para- 
chordal part of cranium; ., 
post-occipital plates, 
