556 
DR. A. G-UNTHER’S DESCRIPTION OE CERATODUS. 
the type of a sixth family. Cercdodus , having the tins lohate in an eminent degree, 
would appear to belong to this suborder ; and therefore I shall attempt to examine the 
affinities of the Dipnoi to some Crossopterygian fishes, and finally, perhaps, arrive at a 
conclusion regarding the limits of this suborder. 
I take first the type of the family Ctenododipterini , viz. the genus Dipterus. 
The materials on which the following observations on Dipterus are based, are exam- 
ples in the British Museum, and especially some most instructive specimens belonging to 
the Museum of the School of Mines in Jermyn Street, and kindly offered for my exami- 
nation by Professor Huxley. Pardee’s excellent Monograph, “ Ueber die Ctenodipte- 
rinen des devonischen Systems,” St. Petersb. 1858, 4to, was my guide in examining 
these materials. 
The characters of Dipterus which appear to indicate an affinity to Ceratodus may be 
described thus : — They are fishes with an elongate body covered with cycloid scales ; head 
depressed, snout obtuse ; dorsal and anal fins thrown back, belonging to the caudal por- 
tion of the vertebral column ; paired fins acutely lobate ; opercular apparatus well de- 
veloped, consisting of two, possibly three pieces. No separate maxillary or intermaxil- 
lary. The bones of the lower part of the skull and the mandible essentially as in Cera- 
todus, only the pterygo-palatine shows a longitudinal groove as if it had consisted of 
two bones. Vertebral column not divided into vertebrae*. The palate and mandible 
armed with a pair of large flat tubercular dental plates, placed as in Ceratodus. To these 
characters, which were previously known, I may add that a specimen in the Jermyn- 
Street Museum (marked 4T), figured on Plate XXXIV. fig. 4, shows clearly the presence 
of a pair of vomerine teeth in Dipterus. These teeth, indeed, are not preserved them- 
selves ; but two small roundish cavities (v), one on each side of the median line of the 
skull, in front of the palatine teeth, indicate distinctly the place where a pair of vome- 
rine teeth were implanted in the cartilaginous substance of the vomer. In the same 
specimen the position of the nostrils (n) is indicated by an accumulation of the matrix ; 
it is the same as in Ceratodus and Lepidosiren. 
On the other hand, Dipterus differs from Ceratodus in being eminently heterocercal ; 
there are two dorsals and one anal fin separate from the caudal ; the scales are covered 
with a layer of enamel, with smooth, porous surface. Head covered with numerous 
scutes with the same surface as the scales ; gular plates behind the mandibulary sym- 
physis. Interneural and interhsemal spines branched at their distal end, to which the 
dermal rays are joined, the latter being branched and jointed. Finally, as regards the 
microscopical structure of the dental plates, the medullary canals are more irregular in 
their course than in Ceratodus ; they frequently anastomose with one another ; the den- 
tinal tubes are coarser, dendritically branched, and less numerous. 
Can any thing be more singular than a combination of such characters 1 If we had 
had the head only of Dipterus with the trunk, we should certainly have seen in it 
* No vertebra bas ever been found in British specimens; and Pandek, who figures vertebrae (which he found 
in Russia) in connexion with this genus, is by no means certain of their correct determination. 
