Pisces. | DEVONIAN VERTEBRATA. 591 
Shortly after appeared the 2nd Vol. of M. Agassiz’ Recherches sur les Poissons Fossiles, in which he refers 
to the above paper (p. 8); but conceiving that the two dorsal fins, which had struck Cuvier as at once dis- 
tinguishing the present fishes from the Palwonisci of the copper-slate, did not really exist, he proposed to change 
the name of the genus to Catopterus, supposing it to have one anal and one dorsal fin. The four species there 
described and figured he also suggested to be imperfectly observed, and proposed to unite them all under the 
one name Catopterus analis (Ag.). He also denies the correctness of the views of Cuvier and of Sedgwick and 
Murchison as to the roundness and imbrication of the scales (p. 24); and stating them to be, on the contrary, 
rhomboidal and flat, he places the genus in the Family Lepidostei. In p. 113 of the same work M. Agassiz 
states that he had examined some of the original specimens figured by the above writers, and that he found his 
corrections as to the continuity of the dorsal fins were not correct, that Messrs. Sedgwick and Murchison had 
correctly described and figured those fins, and that his generic name Catopterus could no longer be retained in 
preference to their Dipterus ; on a second examination he discovered the two anal fins pretty nearly as they had 
figured them, but still retained his view of the form and arrangement of the scales; and now viewing the 
imperfect and doubtful fragment named Dipterus macrolepidotus as the type of the whole, he proposes that the 
three well-known species should be united under that name, on the supposition that the large flat rhomboidal 
plates, figured in the Geological Transactions under the latter name, became converted into the small rounded 
ones, of the more perfect fishes, there noticed (under the other names) by abrasion. This is the more remark- 
able, as at p. 113 (loc. cit.) he refers to the figures given of that species by Messrs. Sedgwick and Murchison 
as examples of his new genus Diplopterus. I have since found this to be truly the case, although in his last 
ichthyological work, Mononographie des Poissons Fossiles du Vieux Gres Rouge, &c., he does not give this 
reference for the Diplopterus, but quotes the Dipteri collectively under the specific name given to these frag- 
ments as above. 
Before recording my own observations I must remark that the above brief réswmé of the literature of the 
genus Dipterus is not intended as a reflection on M. Agassiz—for whose labours no one can entertain a more 
profound respect than I do,—but merely as a necessary record of the various changes which have been proposed 
in the views of the original describers of the genus, and which I believe, after an attentive examination, to 
have been altogether unnecessary, as some of them are already admitted to have been. 
On examining a large suite of the different species of Dipterus described by Prof. Sedgwick and Sir R. 
Murchison, now deposited in the Geological Collection of the University, I find that in all the examples of 
all the species, except the D? macrolepidotus, the scales, when attentively examined, are circular and distinctly 
imbricated; they are marked on the surface with fine, elevated, concentric lines ; 
thickest in the middle and very thin and brittle at the edges, from which latter cireum- 
stances, combined with their quincuncial arrangement, they are of course liable to break 
into a more or less regular rhombic shape when the fish is crushed. This may have 
possibly misled M. Agassiz’ draughtsman, or even himself on a hasty view; but in those 
cases where this rhomboidal appearance is strongest, it will be found that, Ist, the lines 
of the surface are not as Agassiz represents them (Poissons Koss. Pl. 2 a, Vol. I1.), 
quadrangular, and parallel with the margin, but curved. 2nd, These pseudo-rhombic scales are never regular, 
like those of the true Sauroid fishes, but are extremely diverse in shape, and frequently present large notches, 
where one part of a scale has retained its true circular margin, and another part broken straight off, giving 
the deceptive quadrate appearance. Those specimens which, like most of those figured in the Memoir 
quoted, retain their scales comparatively uninjured, with their imbricated rounded margins, are, on the other 
hand, quite regular. But what places the fact of the circularity and consequent imbrication of the scales 
beyond all doubt, is the circumstance that I have repeatedly noticed single scales separated from the body, 
in which the outline was perfectly round; and I subjoin a rough sketch of those various conditions, about 
one-third larger than nature, as seen in a specimen of the D. brachypygopterus. 
Taking for granted, what the suite of specimens in the Cambridge Museum proves beyond a doubt, 
that the scales of the Dipteri are really rounded and imbricated, we find that the genus must be removed 
from the group of Sauroid fishes in which it has hitherto been placed on the supposition that the scales as in 
[easc. ur. ] 4G 
