448 General Notes. 
name being available for the fossil, it may be named Protacanthodes 
Hollardia and Triacanthodes in the oblong caudal peduncle and 
enlarged caudal fin while its physiognomy rather recalls the true 
Triacanthi. The occurrence of a form so closely related to the 
Triacanthodes of the Japanese sea, and to the Hollardia of the 
Caribbean in the eocene seas of Europe, is worthy of special note, and 
this is a sufficient reason for the present communication. 
The nearest extinct associate of Protacanthodes is not Protobalis- 
tum but Acanthopleurus Ag. The two belong to the same family 
but appear to be otherwise distantly related. The other extinct 
genera of Scleroderms, Balistomorphus Gill, Acanthoderma Ag. 1843, 
not Cantraine, 1835, and Bucklandium Koenig— Glyptocephalus 
Ag.) are rather to be associated with the Balistids. 
The exact characters and relations of all these fishes remain to be 
known.— Theo. Gi 
THE PHYLOGENY OF THE Horsss.'—This brochure of 71 pages, 
illustrated by two excellent plates, cannot fail to instruct the student 
who is unfamiliar with this subject. The authoress shows a great 
degree of familiarity with the history of the facts known in this 
connection and they are set forth with considerable fulness of detail. 
She has been more fortunate than some of her predecessors 
in avoiding record in extenso of the mythology of the subject, which 
has been long since consigned to its place in the waste-basket by 
American palzontologists. We allude to the Eohippus, Miohippus, 
and Pliohippus, which still appear occasionally in theological works 
and school-books of America and England. A considerable part 
of the essay is devoted to the endeavor to prove that the genera 
Palzeotherium and Hippotherium must be excluded from the line 
of descent, which has continued from Protogonia puercensis through 
Phenacodus, Hyracotherium, ete., to Equus. he describes and 
figures with much care certain bones of the carpus and tarsus of 
Anchitherium, Hippotherium, and Equus, in evidence of this posi- 
tion as regards Hippotherium. We say with reference to this 
question, that in discussing the phylogeny of genera, one must 
confine himself to generic characters, and it is necessary to ascertain 
what these are in the skeleton before we can use them properly. 
There are some species of supposed Hippotherium of North Amer- 
ica which approach Equus so closely in dental characters that 
the descent of some species of the latter from them looks probable. 
Probably the species of Equus are polyphyletic,? some coming trom 
1 Etudes sur l’Histoire Palzontologique des Ongulés, II, le Developpe 
ment des Equide. Par Marie Pavlow. Moscow, 1888. 
2 I have expressed this opinion in an article on the Perissodactyla in 
American Naturalist, 1887, p. 1076. 
