356 RAMSAY H. TRAQUAIR ON THE 
pose to call Mesolepis micropterus. We have in these specimens the deep body 
and narrow tail pedicle of M. scalaris along with a dorsal fin which is propor- 
tionally less high and acuminate in front than in that species. The mandibular 
teeth are exposed in the specimen belonging to Mr Beresrorp WricHT, and 
these, though the fish is in other respects an undoubted Mesolepis, are, like the 
teeth of Platysomus parvulus, slender and cylindro-conical in shape, and scarcely 
dilated above the root. 
Geological Distribution.—Mesolepis has hitherto been found only in the Coal 
Measures or Upper Carboniferous rocks of Great Britain, and seems to be 
nowhere very abundant as regards number of specimens. The best examples 
of the genus which I have seen are from North Staffordshire, and are in the 
collection of Mr Warp of Longton ; but it occurs also in the coal-fields of 
Derbyshire and of Lanarkshire. 
Structure.—The body is deeply fusiform, deeper than in Eurynotus, less so 
than in Platysomus. The scales of the flank are higher than broad, but 
as Professor YounG has observed, they have not yet assumed the extremely 
high and narrow aspect seen in Cheirodus and Platysomus. As usual, the 
scales become more equilateral towards the dorsal, ventral, and caudal aspects. 
Taking the external aspect of a scale from the front part of the flank (Plate IV. 
fig. 2), its marginal covered area is seen to be very narrow ; the exposed surface 
is quadrilateral and slightly rhomboidal, and is ornamented by raised tubercles, 
frequently running together into sinuous ridges, which are more or less vertical 
in their direction ; from the upper margin, and close to the anterior superior 
angle, there arises a prominent, flattened, and pointed articular spine, marked 
externally by one or two furrows converging downwards towards its base. 
The internal aspect of the scale (fig. 3) is smooth, and presents a vertical keel, 
close to and parallel with the anterior margin, passing above into the articular 
spine, and bevelled off below and behind by the anterior margin of the pointed 
fossette which lodges the spine of the scale next below. It is manifest that 
these flank-scales are conformed exactly upon the so-called ‘‘Lepidopleurid” — 
type, but further back, as for instance opposite the origin of the anal fin, the 
keel or “scale-rib” tends to pass back toward the middle of the scale, 
becoming less marked or even obsolete, while the articular spine and corre- 
sponding fossette appear upon the middle of the upper and lower margins re- 
spectively (figs. 4 and 5). No better instance could be had of the unimportance, 
as a “subordinal ” character at least, of the position upon the scale of these keels 
or so-called scale-ribs. The scales of the body are arranged in dorso-ventral 
bands, whose backward obliquity is rather less than in Hurynotus ; below the 
root of the pectoral fin the most anterior of these turn a little forwards; 
the same condition is observed on the back for a little distance behind the 
occiput. The scales clothing the sides of the caudal body prolongation are 
