i8Sr,] Geology and PalcBontology . 149 
The conclusion is that False ohatteria is one of the Progan- 
osauria, and that it is probably a member of the family of the 
Stereosternidae. The division Proganosauria differs from the 
Rhynchocephalia by the structure of the pelvis. 
Since the above was written, a review of Professor Credner's 
paper, by Dr. G. Baur, appeared in the February number of 
the American Journal of Science and Arts. His conclusions are 
similar to those reached by myself.— E. D. COPE. 
Brogniart and Doderlein on Xenacanthina. Thanks 
to these authors we are now well acquainted with the structure 
of this important type of palaeozoic fish. M. Brogniart^ has 
described the structure of the skeleton, and Professor Doder- 
lein- gives us that of the skull. The former bases his observa- 
tions on numerous specimens from Commentry, and the latter 
on material from the coal formation of Alsace. He shows that 
it is nearly allied to Didymodusfrom the North American Per- 
mian, and represents the same ancestral type of fishes. The 
cranial structure is that of an Opistharthrous shark; that of the 
lateral fins is of a Dipnoan type ; while the characters of the me- 
dian fins are those of a primitive Teleostome, as seen in some 
Crossopterygia. There is a well developed hyomandibular ; 
and the toothed spine, long known as a separate body, and first 
identified by Kner, is articulated with the posterior median 
part of the cranium. The pectoral fin is unsymmetrically bi- 
pinnate, and the ventrals are unipinnate. They arise from a 
lateral cartilage, and terminate in a simple, elongate, fringed 
plate, which is the position of the male organ of the sharks. 
The vertebral centra are unossified, but intercentra and mesial 
spines are present, the former supporting short ribs. The dor- 
sal fin is especially interesting, as displaying one of the primi- 
tive stages of development of this organ. It is distinguished 
by the enormous size of its basiosts, which, as in Lepidosiren, 
are articulated with the axinosts. The fin radii also articulate 
with the baseosts, thus differing from the Lepidosirenidae. and 
agreeing with Pheneropleuron. And all these support with the 
neural spines, confirming the view which I have taken of the 
original relation of the fins to the vertebral column. 
Dr. Doderlein agrees very nearly with the position assigned 
this division (the Ichthyotomi) by the present writer, except 
that he thinks that it should be separated from the Elasmo- 
' Etudes sur le Terrain Houillier de Conmientrv, p.ir C. F-rogniart et E. Sauv- 
