— 201 — 



origins ventral to and bctween tlie optic and trigemiuo-facialis foramina, on the outer surface of 

 that median process of the parasphenoid that McMurrich considers as a basisphenoid completely 

 ankylosed with the parasphenoid, but which Sagemehl ('91, p. 575) considers, in Silurus, as a simple 

 process of the parasphenoid; none of the muscles entering the cranial cavity. It may furthermore 

 here be stated that these muscles are said by Workman ('00) to be innervated as they are in Amia, 

 and hence as I have shown them to also be in Lepidosteus (present werk), and that Ameiurus is the 

 only teleost in which this manncr of innervation has, as yet, been described. 



Ameiurus thus presents conditions siniilar to but even more extreme than those in Lepidosteus, 

 the cross-canal of the latter fish here being a solid bolster, due, quite undoubtedly, to the invading 

 growth of the surrounding cartilage. Yet, the condition in Ameiurus is said (McMurrich) to represent 

 an aborted condition of the teleostean myodome, while that in Lepidosteus is said (Sagemehl) to 

 represent a condition from which that myodome was developed! Wishing to determine which of these 

 two directly opposed assumptions is the correct one, I have consulted the geological record, and, 

 while that record certainly does not give a definite Solution, it has suggested what seems to me such 

 a Solution; for it has led me to ascribe a totally difEerent motive to the origin of the myodome than 

 that proposed by Sagemehl, which, as is well known, is the simple seeking of a better point of origin 

 by one or more of the muscles of the eyeball. 



According to Zittel ('87 — '90), whom I have selected because of the convenient tables given, 

 representatives of the f amilies Siluridae and Ginglymodi, in the latter of which the living Lepidostei 

 are placed, are found in the Eocene forma tions, and no earlier; and in all the living representatives 

 of these two families that have been examined in this connection, there is no functional myodome. 

 Representatives of the family Halecomorphi, in which Amia, with a well developed myodome, is 

 placed, are found considerably earlier, in the Jurassic deposits. Certain other families of the Lepi- 

 dosteidae occur earlier than any of the Amiadae, the Stylodontidae being found in the Dyas (Permian) 

 deposits; but, as two Jurassic representatives of this latter family, Lepidotus and Dapedius, are 

 said by Woodward ('93) to have a ,,basicranial canal" — that is a myodome — it is evident that 

 Lepidosteus can not descend from them, if its myodome represents a primary condition. 



The earliest teleosts are said by Zittel to be the Hoplopleuridae and Clupeidae, both of which 

 are said to be found in the Triassic, considerably earher than the families Siluridae and Ginglymodi, 

 and as early, even, as any representatives of the order Lepidosteidae excepting only the Stylodontidae. 

 Of these two famihes of teleosts the Hoplopleuridae are extinct, while the Clupeidae are well represented 

 by living species, several of which, Clupea, Elops, Albula and Megalops, are known to have a well- 

 developed myodome. In Clupea harengus, which I have examined for this purpose, the proötic bridge 

 is thick and has a bevelled anteri-or edge which slopes antero-ventrally, the whole bridge much 

 resembling that of Gadus excepting that it lies in a horizontal instead of a strongly inclined position. 



Several other families of teleosts existed at the beginning of the Cretaceous period, and hence 

 earlier than the Ginglymodi and Siluridae. These families are the Saurocephalidae (extinct), Strato- 

 dontidae (extinct), Salmonidae and Scopelidae. all placed by Zittel in his order Physostomi; the 

 Labridae and Chromidae of his order Pharyngognathi ; and the Berycidae, Sparidae, Xiphiidae, 

 Carangidae, Cataphracti, Gobiidae and Aulostomi of his order Acanthopteri. In living represent- 

 atives of these several families, Parker shows a myodome in Salmo salar, of the Salmonidae; in 

 Dactylopterus and Peristedion, of the living Cataphracti, I have described it in the present work: 

 in Gobius of the Gobiidae, a myodome similar to that in Dactylopterus is found, as also already 



Zoologioa. Heft 57. 2G 



