^'^'iH-ii'^'] PROCKEDING.S OF THE NATIONAL MUSEUM. 455 



iiicliided til is order in 1 1 u* C rosso] ttcrv^nii with doubt * o\\ tlu' siiijposition 

 lliat tlicy iK)ss('ss ;i maxillary arch and susiteiisoriuin. The loriiier is 

 however not described so ;is to distinguish it from ii i)alatoi>terygoid 

 arch by authors, and no evidence of the existenco of such an arch can 

 be derive<l from American forms. Advance sheets of volume ii of 

 the Catahtgne of Fossil Fishes in the Britisli Museum, by A. Smith 

 Woodward, show that this able authority i)laces the Placodermata in 

 the Dipnoi, thus indicating that they [)Ossess neither maxillary arch 

 nor suspensorium. 



There is much in the structure of the skull of Macropetalichthys to 

 confirm this oi)inion. The nuchal portion of the structure with its hit- 

 eral nuclial elements is represented by the cartila'ginous mass which 

 extends posterior to the median occi[>ital bone in Ceratodus, in which 

 (his region has very much the form of the nuchal shield in Macropetal- 

 ichthys, although it is relatively shorter. The chordal groove with its 

 descending lamime resembles much the i)roduced occii)ital bone of 

 Lepidosirem. The parasphenoid in both T>epi(h)sirem ami Ceratodus are 

 piodnced posteriorly abnormally, and it is only necessary to imagine 

 this part toberecbiced to its normal length to have the conditions found 

 in Macropetalichthys. The broad parasphenoid and vomer remind one 

 of that of Ctenodus. As I have shown that Macropetalichthys is allied 

 to Diniehthys, we can add in favor of the supposition of allinity to the 

 1 )ipnoi the i)eculiar dentition of that genus. The eetetramerous t struc- 

 ture of the dorsal fm shown by Von Koenen and Traciuair to exist in 

 Coccosteus, and shown to be probably present in Diniehthys by New^- 

 bcriy, are in favor of the Dipnoan theory. Elements supposed to be 

 ihe axial elements of i)ectoral fins are described by Dr. Newberry. 

 These are simple and without lateral articulations, and are thus of the 

 iinibasal type which is general in Dipnoi as well as in some Crossop- 

 terygia and all JJhipidopterygia. They somewhat resemble those which 

 I shall describe in this paper as characteristic of Megalichthys. It is on 

 account of this part of the structure that the Artlirodira can not be 

 arranged near to the sturgeons, where Macro})etalichthys has been 

 placed by Newberry and others, to sa\' nothing of the cranial structure, 

 which has no resemblance to that of those fishes. 



I first referred Macropetalichthys to the Placodermata (Arthrodira) 

 in a review of Professor Newberry's work on the Paleozoic Fishes of 

 North America in the American Naturalist for September, 18!M); and 

 this view has been adopted by Mr. A. Smith Woodward as above 

 mentioned. 



ISp<Tirs of MarropcidUchtJiys. — It is evident that the two crania which 

 1 have described in the preceding pages belong to two different species. 

 The larger is the .1/. riiplnidohihis of Owen, and the smaller the M. 

 sullivantii Newberrv. In the latter the nuchal element and its included 



' Synopsis ofthe Families of Mio Vi rtfltrata, American Naturalist, October, 1869. 

 t Copt', American Natnralist, ISDO, p. IKi. 



