PISCES. 
83 
Thursius , and Glyptolcemus are Devonian Crossopterygians 
with obtusely lobate pectoral fins, rhombic scales, and teeth 
of simpler structure (Wall-case 6, Table-case 11). Megal- 
ichthys , also with rhombic enamelled scales, comprises some 
relatively large species of Carboniferous and Lower Permian 
age, and its remains are among the commonest fossils of the 
Fig. 86.—Restoration of Osteolepis macrolepidotus, from the Middle Old 
Red Sandstone of Scotland ; one-third nat. size. (After R. |H. 
Traquair. Wall-case 6.) 
English Coal Measures (Wall-case 6, Table-case 11). Rhizodus 
is a still larger fish with deeply-overlapping round scales, 
from the Lower Carboniferous. Some of the large teeth and 
jaws of Rhizodus hibberti from the Lower Carboniferous of 
Scotland in Wall-case 6 probably belong to fishes 9 or 10 feet 
in length. Strepsodus (Eig. 87) and Rhizodopsis are allied 
genera, whose teeth and scales are common coal fossils. 
The Ccelacanthidse (“ hol- 
low-spined ”) are the most 
remarkable Crossopterygians, 
ranging almost 
unchanged 
from the Upper Devonian to 
the Upper Chalk (Wall-case 7, 
Table-case 12). Their name 
refers to the circumstance that 
the spines of the backbone are 
only superficially ossified and 
so appear hollow when fossil¬ 
ised. Their general appear¬ 
ance is shown by the accom¬ 
panying drawing of Undina 
(Fig. 88), which is represented 
in Table-case 12 by fine specimens from the Upper Jurassic 
Lithographic Stone of Bavaria, and from the Lower Lias 
of England. The large air-bladder seen beneath the back¬ 
bone in many specimens, especially in those from the 
Chalk, has a thin bony wall, as in some existing fresh- 
G 2 
Fig. 87.—Tooth of Strepsodus 
sauroides , from the English 
Coal Measures ; nat. size. 
(Table-case 11.) 
Wall-eases 
5-7. 
Table-cases 
11 , 12 . 
Wall-case 
7. 
Table-case 
12 . 
