A FISH BRAIN FROM THE COAL MEASURES 151 
In the Coal Measures fish the eminences here provisionally 
identified as tubercula acustica are unlike those of any of the 
existing Ichthyopsida, though they resemble most closely those 
of the teleostean species in which the tubercula acustica fuse 
dorsally above the fourth ventricle. The anterior eminences 
may correspond with the ganoidean lobi lineae lateralis, in this 
case crowded medialward and fused above the ventricle. 
The cerebellum of the Coal Measures fish resembles closely 
that of Rhadinichthys from the Mississippian. Its form is 
unique, resembling no cerebellum known among recent fishes, 
though it is not far from that of the closest recent relative of 
these species, the sturgeon (Acipenser).”?!. Dr. Johnston has sug- 
gested to me that the medial portion may be involuted between 
the optic lobes in the form of a valvula cerebelli, as in Acipenser 
and teleosts. 
The optic lobes are teleostean in their large size, as is at once 
evident from an examination of the figures The eye was ex- 
tremely large as indicated by the bony orbit, well preserved in 
a median fracture of one of the nodules (fig. 17). The orbit, as 
shown by the impression figured, is slightly oval and measures 
8.25 mm. in antero-posterior diameter. Its large size probably 
accounts in part for the unusual development of the optic lobes. 
The relations of the optic lobes to the hypothalamus and cere- 
bellum and their dimensions are best discerned from an exami- 
nation of the figures (figs. 16, 17). The optic nerves were evi- 
dently short, as is apparently determined from an examination 
of the one orbital region which is at all well preserved. Ap- 
parently the optic nerve entered the orbit acentrally. The po- 
sition of the optic chiasm has been indicated in one of the figures 
(fig. 16) and it is recognized by its contour on the surface of 
the brain. It cannot be accurately described from the present 
material, however, except that its position is as indicated, an- 
terior to the lobus inferior. 
Lying between the optic lobes, the lateral lobes of the cere- 
bellum and the anterior pair of eminences termed ‘tuberculum 
*1 See Johnston, J. B. The brain of Acipenser. Zool. Jahrb., Bd. 15, 1901, 
plate 2. 
