Reviews—Fritsch’s Paleozoic Dipnot. 525 
indistinct on the first rib, and, notwithstanding the difference in the 
length of the ribs, the others all have an equal number of outwardly 
directed cusps. The smallest examples exhibit five cusps on each 
rib, the largest, seven to nine. In very old teeth, the inner crimpings 
become indistinct. With increasing age, also, the dental plate 
becomes arched; while the smallest young teeth are comparatively 
flat, the largest old examples appear arched above, as shown by a 
comparison of the profile figures. The small dental plates corre- 
spond to those that have been named C. elegans, H. and Atth., in 
England ; the Jarge ones agree with C. obliquus, H. and Atth.” No 
vomerine teeth have hitherto been detected in Bohemia, and figures 
only of an English specimen are thus given. Some remarks are 
made upon the microscopical structure of the teeth, with illustrative 
drawings of sections; and it is pointed out that in the vasodentine 
of Ctenodus the vessels are more branched and anastomosing than 
in Ceratodus. 
Proceeding to a discussion of the axial skeleton of the trunk, Dr. 
Fritsch considers that there is evidence again of an extremely close 
approximation to Ceratodus. The notochord seems to have been 
persistent, with slight ossifications in the sheath; and the first rib 
is considered to have been relatively very stout, as in the existing 
genus. Many of the ribs show traces of having been broken and 
repaired during life. 
The brief sections upon the appendicular skeleton bear witness 
once more to the laborious and exhaustive character of the investi- 
gations made by Dr. Fritsch in regard to the most unpromising 
fragments. None but isolated bones of the limbs and their support- 
ing arches have hitherto been discovered ; but an attempt is made 
to restore the pectoral arch—consisting of a greater number of 
elements than that of Ceratodus; and again, attention is directed 
to the high degree of ossification of all the parts. 
The last plate is devoted to an interesting comparison of the 
scales with those of Ceratodus. The outer side of each scale 
“appears smooth in the middle, and is only seen to be rugose when 
highly magnified. The border exhibits concentric lines of growth, 
of varying width, parallel to the margin. Across these extend small 
parallel ridges, on the middle of which are rows of minute pits, 
apparently indicating the spots that originally supported denticles.” 
Another noteworthy feature is the forked appearance of the sensory 
canal upon a detached scale of the lateral line—a condition unknown 
in Ceratodus. 
As the result of his researches, Dr. Fritsch considers that the 
Bohemian examples of Ctenodus obliquus must have attained a length 
of about 140 centimetres. ‘The greater number of the dermal 
bones in the skull, added especially to the stronger ossification of 
the entire skeleton than in the case in Ceratodus, parallels what we 
have observed among the Permian Amphibia, which also have the 
skull better armoured than their now living allies.” 
Ctenodus applanatus, Fritsch, is defined as having flattened upper 
teeth, only twice as long as broad, with sharp but scarcely crenated 
