9i6 The American Naturalist. [October, 
possibility of separate cartilaginous neural arches. The parietal mus- 
culature and the peripheral nervous system (except the three higher 
sense nerves) are segmented in the head as in the body region. The 
number of head myotomes is in general nine, and in those Craniata 
which have no hypoglossus as a cranial nerve (unless the same and its 
myotome is aborted), is smaller. To each body and head segment 
belong a dorsal and a ventral nerve. These are primitively separate, 
as is shown by Amphioxus and the embryos of the Craniata. In case 
the ventral nerve is lacking, the corresponding myotome is lacking. 
The vagus is a complex of two nerves. There is no ground for the 
view that the Craniata ever possessed more than eight gill pouches 
(apart from one possibly aborted in the hyoid arch). This number is 
reached in Heptanchus, Chlamydoselachus, the embryos of the Petro- 
myzons and probably in the Carboniferous genus Xenacanthus. 
Horny Teeth in the Marsupialia. — Teche, in studying the 
skull of a young Myrmecobius {Anat. Anzeiger, Aug., '89) finds that a 
bony ridge runs parallel on either side to the alveolar process of the 
upper jaw, while in older skulls it exhibits a retrograde development. 
In sections of the mucous membrane covering this ridge, he found 
several clusters of tooth-like structures, which upon examination with 
a higher power were resolved into a large number of rows of teeth, 
each containing several (as many as 8) horny teeth, nested within each 
other. In older Myrmecobii no traces of the teeth were found. 
On the Genus Clevelandia.— In the Naturalist for Jan., '90, 
page 85, occurs the statement that " Clevelandia is reduced to synon- 
omy (by Jenkins and Evermann, Proc. U. S. Nat. Mus., 1888), as was 
done some time ago in this journal." 
The genus Clevelandia was based on a specimen in the collections 
of the Museum of Comparative Zoology, and the diagnosis published 
in the Proceedings of the Calif. Acad. Sci., second series, Vol. L, 
Jan., '88. 
At the time the diagnosis was written we could not, on account of 
Museum regulations, examine the skull of the type of Clevelandia. 
Later, Mr. Evermann sent us specimens of his Gillichthys guaymasia, 
requesting us to re-examine the type of Clevelandia. We did so, ex- 
amining the skull, which was found to be smooth and regularly convex 
in transverse profile, without ridges or crests. The skull of Gillichthys 
is i^epressed, with a strong median crest. These notes were sent to 
Mr. Evermann. This was in .the early part of the summer of '88. 
