Pe 56 [May 20, 
of the jaw. The opposite margin is a little more elevated and is more 
closely anchylosed to the base of the tooth. The crown is conic, subround 
in section, and curved backward. There are no cutting edges, and the 
base is a little flattened in front and in behind. On each of the faces thus 
formed, there is an open, shallow groove, sometime obsolete. There are 
no other grooves nor sculpture on the teeth. 
Each specimen of this tooth is single, and anchylosed to the same (cor- 
responding) part of the jaw. The tooth is at one extremity of the alveolar 
groove ; above the opposite end is the basis of a bone attached at right 
angles (? prefrontal or malar). One of the specimens displays an extensive 
pulp cavity. 
Wen thVorycrowihs-ceccectectase se ieee dshiiseatowcanehe SOCERCSESE .010 
Diameter at base....... avwaesces eapiededaeseisienses de sines otests eae ta bie ice 004 
ACTINOPTERI. 
In the transactions of this Society, published in 1871, and more fully in 
the Proceedings of the American Association for the Advancement of 
Science, at the meeting of 1871 (published early in 1872), I showed that 
the supposed order of Ganoids as defined by Miller, is not a homogeneous 
or natural association of types. I pointed out that the recent genera must be 
distributed between two divisions of fishes of high rank, viz.: the Crossop- 
terygia, and the Actinopter?. The last-named division was believed to in- 
clude the fishes previously known as Chondrostei and Teleostei. Some of 
the so-called Ganoids of Miller and Agassiz were referred to different sub- 
divisions of the Actinopter?. In a paper recently published in the Pro- 
ceedings* of this Society, a better expression of natural affinities was 
thought to be obtained, by regarding the Crossopterygia, the Chondroste?, 
and the Actinopter?, as forming a single sub-class of the class Pisces, under 
the name of Hyopomata, the other sub-classes being the Dipnoz, the 
Selachia, and the Holocephali. ' 
I had already referred Phaneropleuron+ to the Dipnot, when Dr. 
Ginther’s and Prof. Huxley’s researches into the structure of Ceratodus 
forsterii led them to place this genus also in the same sub-class. Ginther 
also refers the fossil genera Dipterus, Chirodus and Conchodus to the 
Dipnoi, and with these must go Ctenodus and its immediate allies. The 
Polypteridw and Celacanthide, which were arranged by Huxley, with the 
preceding forms in his sub-order Crossopterygia,{ are clearly Hyopomata, 
having well developed hyomandibular and maxillary bones, as well as 
characters of the pectoral fins equally wanting to the Dipnot. It is thus 
evident that the division Crossopterygia, as left by Huxley, cannot be 
maintained, but that it must rest entirely on the definitions given by me 
in the papers above quoted, where the two families mentioned were the 
only ones referred to it. It is possible that a strict adhesion to the law 
* May, 1877. . 
+ Transactions American Philosophical Society, XIV, 1871, p. 450. 
* Memoirs of the Geological Survey, Great Britain, Decade X. 
