ANIMALS. 229 
Platysomus to the family of the Pycnodonts; but there are other points in the 
structure and form of the fish which sanction the propriety of the change. The 
deep and flattened form of the body induced MM. de Blainville and Germar to 
arrange it with the Stromatei, and evidently engendered a doubt in the mind of 
Professor Agassiz as to the validity of the zoologicial position he assigned to it. The 
principal structural peculiarities he so clearly points out have, he says,’ a greater 
affinity to Pycnodus and Gyrodus than to Paleoniscus and Caturus. On the receipt of 
the Ferry Hill specimen, feeling unwilling to trust my own imperfect judgment on a 
point of so much importance, I informed Agassiz of the reasons which induced me to 
propose the alteration, and the following passage from his answer fully authorises the 
change :—‘“I quite agree with you in the propriety of combining the genus Platysomus 
with the Pycnodonts ; for some time past I had indeed been impressed with the grea. 
difference there is between that genus and the others of the family in which it stands, 
and I now feel that my only reason for putting it there was the heterocerca]l form of 
‘tail, a character which could not fail to produce a vivid impression upon my mind 
when first discovered, but which I now expect to find in fishes of various families in 
the oldest geological ages, as well as everywhere in the youngest state of our actual 
fishes in their embryonic growth. ‘The teeth, as you mention, are conclusive evidence 
for placing Platysomus with the Pycnodonts. Let me now point out to you another 
evidence of this relation in the form of the skeleton, especially of the apophyses 
before the dorsal. The specimens of Platysomus in the Museum in Munich show 
some good portions of the skeleton, and m my mind I can now compare them to the 
skeleton of the small Pycnodus rhombus, without detecting any difference. Pray 
institute the comparison upon a safer ground than recollection, and let me know what 
you find. You know under what circumstances the fossil fishes have been worked 
out, and as a matter of course I must expect to see daily important additions made to 
the edifice of which I have laid only the foundation.” It is needless to go over the 
anatomical details so fully described in the article on the Genus Platysomus in the 
‘Poissons Fossiles;’” suffice it to say, that I had instituted the comparison recom- 
mended by Agassiz before I wrote to him on the subject, and had fully satisfied 
myself that in the generic characters it approached very closely to Gyrodus and 
Microdon, and only differed from the Pycnodonts hitherto known in having a decided 
heterocerque tail. It will be necessary for me to say a few words with reference to 
the ‘apophyses before the dorsal,’ alluded to in the above letter, since I have formed an 
opinion as to their nature at variance with that entertamed by Agassiz. ‘These bones 
are minutely described in the article on the Genus Pycnodus,’ and the question is there 
! Poissons Fossiles, vol. ii, p. 162. 
2 Tbid., p. 161. 
3 Tbid., p. 184. 
