Miscellaneous. 421 
cerceity is more distinct ; and, finally, in the genus Dipterus the 
heterocercal character becomes strongly marked. 
The parallelism between the fossil genera and the embryonic 
stages of the existing osseous fishes is still more striking if we ex- 
amine forms such as Phaneropleuron and Tristichopterus, in which 
the tail is lobed, the dorsal column penetrating into the dorsal lobe, 
-as in the young Pleuronectes. The genera Acanthodes, Diplacanthus, 
Cheirolems, &c. of the Old Red Sandstone represent the stages of 
Pleuronectes in which there is a first indication of the separation 
between the true caudal and the embryonic caudal. 
In the subsequent modifications of the tail in fossil fishes there 
is a tendency to the gradual diminution of the embryonic or supe- 
rior lobe, and to the predominant development of that which is to 
become the caudal lobe proper. 
On comparing the most ancient forms with the genera Plutysomus, 
Semionotus, Lepidotus, and, lastly, Pachycormus, we recognize, as in 
the development of the Teleostei of the present epoch, a gradual 
approach to an externally homocercal tail. 
To these facts, demonstrating the parallelism that exists between 
the embryonic and the paleontological development of the tail, Mr. 
Agassiz adds others derived from characters of ancient Ganoids 
which recur in the embryos of the Teleostei. 
If we wish to formulate the conclusions of Mr. Agassiz in Hiicke- 
lian language, we may say that they supply a fresh proof in favour 
of the law according to which “ ontogenesis is the abridged and 
rapid recapitulation of phylogenesis.”—Proc. Amer. Acad. of Arts 
and Sci. vol, xiii. October 1877 ; Bibl. Univ. March 15,1878, Arch. 
des Sci. p. 368. 
On Selaginopsis, Polyserias, and Pericladium. 
By M. C. Mrrzscuxowsxy. 
According to Mr. Norman’s “ Note on Selaginopsis (= Polyserias 
Hincksit, Mereschk.) and on the Circumpolar Distribution of certain 
Hydrozoa,” which appeared in the ‘Annals’ for March 1878, my 
genus Polyserias had been previously described by Prof. Allman 
under the name of Selagmopsis (Journ. Linn. Soe. vol. xii. 1876); 
hence the species that I described in the last number of this Journal 
must be named Selaginopsis mirabilis, Verr., and Selaginopsis 
Hincksti, mihi. However, I am not yet quite certain of this: and 
unfortunately it is impossible for me at present to verify Mr. Nor- 
man’s opinion ; for in the whole Russian empire there does not exist 
vol. xii. (1876) of the Journal in which Prof. Allman has published 
his diagnoses. The Academy of Sciences of St. Petersburg does not 
receive this journal at all; and the Public Library only possesses it 
down to the year 1875. 
It seemse specially doubtful to me whether the genus Pericladium 
is really distinct from Selaginopsis; and perhaps it would be better 
to retain under the name of Polyserias, proposed by me, a genus 
which would combine Allman’s two genera, and more particularly 
