354 
A. M. REESE 
the cranial and occipital of each side, is the aural canal {au)j 
which may be considered as consisting of two lateral portions 
extending mediad and uniting at the mid-dorsal line. The point 
of union is caudad to the lateral ends of the canal, giving the shape 
of a wide V, when viewed from above (fig. 2, au). From the point 
of this V, Garman ('88) describes a short, median canal extending 
about half-way back to the base of the dorsal spine; he calls it 
the post-aural. This canal, since it was present in less than a 
third of the specimens of C. colliei examined, has been shown in 
the dorsal view by a broken line (fig. 2, pa). Garman does not 
figure the post-aural in either Callorhynchus or Harriotta. In 
the specimen of Harriotta described by Garman the aurals do not 
meet in the mid-dorsal line, but overlap for about half their length; 
he does not say whether or not this is the normal condition, and 
other figures of the animal, at hand, do not make clear this point. 
The lack of fusion in this case would seem to justify the assump- 
tion that there are two lateral aurals rather than a single canal. 
Extending cephalad, along the top of the head, from the point 
of confluence of the occipital and aural canals is the cranial 
canal (figs. 1, 2, cr). From their points of origin the two cranials 
diverge shghtly, then converge somewhat, in the region of the 
orbits; then, after a second • slight convergence, in front of the 
orbits, they converge gradually till they pass over the tip of the 
snout. On the medial side of each cranial canal, in the region of 
the orbits, is a considerable number of fine pores; and on the 
lateral side of each canal, just anterior to the orbital region, are 
half a dozen or more pores of larger size, like those mentioned in 
connection with the occipital and suborbital canals. 
The anterior portion of the cranial canal, where it passes out 
over the snout, has been called the rostral (figs. 1, 2, r). There 
is nothing to indicate where the cranial should end and the rostral 
begin, unless we consider the rostral to be that part of the canal 
where the enlargements, like those noted in connection with the 
suborbital canal, are found. Passing over the end of the snout 
the rostral meets the suborbital and becomes the subrostral. The 
course of the cranial and rostral canals is strikingly alike in all 
the Chimseroids, as far as can be determined by the examination 
