316 
TELE0ST01I1. 
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 , I. S. Newberry, Trans. New York Acad. Sci. 
vol. ii. (1883), p. 147, and Palasoz. Fishes N. America 
(1889), p. 164, pi. xiv. figs. 1, 2.—Cleveland Shale ; Erie 
Co., Ohio. 
Mylostoma variabile , J. S. Newberry, ibicl. (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. TELEOSTOMI. 
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 lamelke. In the living forms— 
ovaries with numerous small ova. 
Order I. CROSSOPTERYGII. 
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, 7 
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