STKUCTUEE OF CERTAIN PALEOZOIC DIPNOI. 199 
the bones of the snout region have almost or quite disappeared, and the 
" parietal " and interi'rontal cover the whole median tract of the top of the 
head. 
The compression of the lateral bones of the skull-roof brought about by 
this expansion of two of the median bones appears to have resulted in corre- 
sponding degrees of disappearance or fusion. Thus in Sagenodus there is 
only one pair of bones in the frontal region as compared with two in 
Ctenodus and three or more in Dipterus platyceplialus. Ceratodus is extreme 
in this respect as in the others : all the bones of the frontal, temporal, and 
tabular regions on each side seem to be represented as a rule by a single 
■ossification. 
Conchoponia, another Dipnoan appearing late in order of time and de- 
scribed below, furnishes an interesting parallel to Ceratodus. Though none 
of the processes have gone as far as in Ceratodus forsteri, yet the two median 
bones are greatly expanded, the bones of the snout much reduced, and 
those of the lateral part of the roof extensively fused. 
Several of the minor characters of the bones of the head in Ceratodus 
as compared with those of Sagenodus are plainly correlated with one another. 
The side-to-side arching of the skull-roof, bringing the squamosal region 
far down on the side of the head, is connected with the reduction in size of 
the operculum^ and also with the shortening of the quadrate. 
CoNCHOPOMA GADiFORMis, Kner. 
The rare fish from the Lebach Shales (uppermost Carboniferous) of 
Saarbruck, called Concliopoma gadifomis by Kner, has never been at all 
adequately described. There is in Edinburgh a very large individual, pre- 
served in an ironstone nodule, which makes the structure very nearly com- 
pletely known. It was prepared by softening the already rotted bones with 
dilute acid and removing the residue by brushing. Casts from the moulds so 
left show all surface details extremely well. 
The general morphology will be obvious from fig. 29, p. 198. The 
skull has the usual Dipnoan structure of an extensive cartilaginous neural 
cranium, which seems to have been considerably ossified in the exoccipital 
region. The head is rocrfed by a continuous shield of membrane bones, 
which, although now flat, seems from its cracked condition to have been 
originally considerably curved. This shield consists posteriorly of a row of 
three bones, of which the median "parietal" is longer than the lateral 
tabular. The " parietal ■" has a low median ridge on its visceral surface ; the 
"tabulars" are concave ventrally and now no signs of attachments. 
The " parietal " articulates with a median interfrontal, and these two bones 
have long lateral attachments to the very large bones which include the 
