1080 The American Naturalist. [December, 
parts now under review are occupied with the Ichthyotomous Elas- 
mobranchii, while the third contains the Acanthodian Elasmobranchs 
and the Teleostomi of the superorder Actinopterygia. 
The descriptions of Ichthyotomi cover several species which the 
author refers to three genera under the names Orthacanthus Agass. 
Pleuracanthus Agass. and Xenacanthus Goldfuss. The material at Dr 
Fritsch’s disposal is excellent, and he elucidates thoroughly the struc- 
ture of the fins of all these forms, and is able to identify the spines and 
teeth of the different species. We are enabled through the kindness of 
Dr. Fritsch to give a figure of the Xenacanthus dechenii from his work. 
Thanks to his labors the greater part of the skeleton of these remark- 
able forms is now well known. There remains some doubt whether the 
forms distinguished as different genera do not belong to a single genus, 
as the characters pointed out by Dr. Fritsch to be distinctive in the 
spines and teeth seem to be specific rather than generic, as has been 
already argued by Mr. Smith Woodward. If the divided terminal rays 
of the paired fins of Xenacanthus dechemii are not dermal, and only . 
absent from the fins of the other forms by accident, as appears to be 
the case, then Xenacanthus must be regarded as a genus distinct from 
the other forms. Dr. Fritsch does not adopt the order Ichthyotomi, 
but his reasons for this course are not. clear. 
The subclass Teleostomi is adopted by Fritsch, who states that he 
does not regard the division of * Ganoidei" as well founded. In this 
he is in accord with views which I have advocated since 1871, in the 
face of almost universal opposition. I can only say that paleontologic 
discovery has long since demonstrated the correctness of this position, 
and its general acceptance cannot be long delayed. Fritsch remarks 
that Smith Woodward adopts my order of Ichthyotomi with a new 
definition, as though it were the division proposed by Cope. But he is 
evidently not aware that I redefined the order, on the basis of the dis- 
covery of the fin structure by Sauvage, in a synopsis of the Families of 
Vertebrata published in the American NaTURALIST for Oct.,:1889, 
with which the later definition of Woodward in the Catalogue of 
Fishes of the British Museum (1891) nearly agrees. 
_ The only form of Actinopterygian fish described, is the genus 
"Trissolepis, which is referred to the Chondrostei. It possessed a rapto- 
rial dentition of acute teeth, and scales of both ctenoid, cycloid and 
ganoid forms, the last on the caudal region only. The following figure 
from Fritsch's work represents this interesting form. 
Of Acanthodii, species of the genera Traquairia, Protacanthodes, 
and Acanthodes are described ; the first two genera being new to science. 
* 
