D4: Sir Philip Egerton on the Tail of Diplopterus. 
gret to be again obliged to notice an omission no less unjust to 
Professor Agassiz. In the November Number of the ‘ Annals,’ 
Mr. M‘Coy, when treating of the tail of Diplopterus, says :-— 
“M. Agassiz has described the species of this genus as having 
heterocercal tails,” leaving it naturally to be inferred, that these 
fishes had the ordinary form of tail common to many of the older 
ganoids. He then proceeds to state, that so far from this beg 
the case, “there is almost as great a development of fin-rays 
above as below the spinal prolongation.” This form of tail, in- 
termediate in appearance between the homocercal and hetero-. 
cereal types, he proposes to style “diphycercal.” The following 
passage from the ‘ Fossil Fishes of the Old Red Sandstone,’ p. 54, 
shows how fairly! Agassiz’s description has been stated by Mr. 
M‘Coy in reference to this modification of the caudal fin :— La 
eaudale a une conformation des plus singuliéres. I] va sans dire 
qu’elle est hétérocerque, et que la masse principale des rayons 
est insérée sous le prolongement relevé de la colonne vertébrale ; 
mais au bord supérieure il y a au lieu de fulcres de véritables 
rayons, en grande quantité, si bien que le prolongement de la 
colonne vertébrale se trouve garni de rayons’ en haut comme en 
bas.” Fig. 1. of tab. 18 gives a very good representation of the 
peculiarity described in the text. Now although the more per- 
fect specimens examined by Mr. M‘Coy may have enabled him 
to trace this modification to a greater extent, yet, in all fairness, 
he ought to have alluded to the facts established by Agassiz in 
the passage quoted above. I prefer again to attribute this seem- 
ing unfairness to forgetfulness of Agassiz’s writings, rather than 
to intentional disregard of them, an opinion which is strengthened 
by the occurrence in Mr. M‘Coy’s writings of the cancelled spe- 
cific appellation Jatus, when speaking of Coccosteus decipiens. 
The remarks on the gradations of structure between the two 
types of tail, appended in a note to Mr. M‘Coy’s paper, and 
stated to have been also noticed by Miller, were made by the 
Professor so long ago as 1844, so that his claim to priority and 
not only to simultaneity of discovery is unquestionable. In con- - 
clusion, I must beg to disclaim any the slightest intention of 
giving annoyance to Mr. M‘Coy, or of underrating in any degree 
the value of his ichthyologic investigations. J am only anxious 
that justice should be done to those who through absence are 
unable to vindicate their own rights until it may be too late to 
do so with effect. . 
I have the honour to be, Gentlemen, your obedient servant, 
Puitrp pE Maras Grey Eeerton. 
