ANIMALS. 229 



Plaii/somus 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 Fyciiodus and Gyrodus than to Palaonisciis 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 Flatysomus 

 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 heterocercal 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 Platysovms 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 in 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 Platysomics 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 i-eference 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 entertained 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 Ibid., p. 161. 



3 Ibid., p. 184. 



