﻿316 TELEOSTOMl. 



discovered hitherto in the Lower Carboniferous of the United States. 

 Two species are recognized, the type specimens being preserved in 

 the Museum of Columbia College, New York. 



Mylostoma terrelli, J. S. Newberry, Trans. New York Acad. Sci. 

 vol. ii. (1883), p. 147, and Palaeoz. Fishes N. America 

 (1889), p. 164, pi. xiv. figs. 1, 2.— Cleveland Shale ; Erie 

 Co., Ohio. 



Mylostoma variabiles J. S. Newberry, ibid. (1883), p. 146, and 

 ibid. (1889), p. 165, pi. xv. figs. 1-5, pi. xvi. figs. 1-4 — 

 Cleveland Shale ; Sheffield, Ohio. [The type species.] 



Possibly in this family may also be placed the tooth from the 

 Devonian of the Eifel, named Typodus glaber, H. von Meyer, Palae- 

 ontogr. vol. i. (1847), p. 102, pi. xii. fig. 2. 



Subclass V. TELEOSTOMl. 



Skeleton more or less ossified, with well-developed membrane- 

 bones : margin of jaw with membrane-bones above and below. 

 Mandibular suspensorium articulated with the cranium ; gill-clefts 

 feebly separated, opening into an external cavity covered by a bony 

 operculum. Membrane-bones of pectoral arch connected with those 

 of the occiput. Exoskeleton, when present, consisting of true bone 

 or delicate, superposed, calcified lamellae. In the living forms — 

 ovaries with numerous small ova. 



Order I. CEOSSOPTERYGII. 



Paired fins lobate, having an endoskeletal axis, more or less 

 fringed with dermal rays ; caudal fin diphycercal or heterocercal. A 

 pair of large jugular plates, sometimes with small lateral plates and 

 an anterior azygous element, developed in the branchiostegal 

 membrane between the mandibular rami. In the living forms — 

 optic nerves not decussating, but forming a chiasma; intestine with 

 a spiral valve. 



