602 



PISCES. 



[MEC. ONY. 



developed, with their apices directed up- 

 ward, and especially in their upper 

 part, where they gradually increase in 

 size, forming strong, more or less de- 

 flected hooks, transversely carinated ; 

 intercostal spaces minutely ridged and 

 striato-punctate ; base moderately in- 

 serted, forming a comparatively thin 

 plate, more or less laterally expanded 

 posteriorly from the angular ridge in 

 front, with more or less prominent 

 marginal angles behind ; pulp-cavity 

 moderately large, similar in section to 

 the body, and occupying the posterior 

 two-thirds of the spine. In costation 

 and the expanded base it is like Ama- 

 canthus, but distinguished in all other 

 respects. Type M. rectus. 



FiQ. 1147. Marracanthus rectus. Anterior part 

 of spin e. 



rectus, Newberry & Worthen, 1866, (Ho- 

 macanthus (?) rectus,) Geo. Sur. 111., vol. 

 2, p. 115, St. Louis Gr. 

 MECOLEPIS, Newberry, 1857, Proc. Acad. Nat. 

 Sci., vol. 8, p. 96. [Ety. mekos, large; 

 lepis, a scale.] Heterocercal lepidoids 

 of small size ; body fusiform ; head ob- 

 tuse ; tail elongated ; lobes unequal ; 

 fins small, provided with delicate fulcra ; 

 dorsal opposite anal, both far back on 

 the body ; crania corrugated or tu- 

 berculated ; opercular maxillary and 

 hyoid plates ornamented ; scales smooth 

 or ornamented; posterior margin ser- 

 rated ; scales of median line crenulated ; 

 two rows of scales extending back to 

 near anal fin ; teeth conical, short, 

 brush-like. Distinguished from Palseo- 

 niscus by small size, posterior position 

 of dorsal fin, and the high lateral scales. 

 Type M. corrugata. Probably a syn. 

 for Palseoniscus, but not figured, and 

 species poorly defined. 



corrugata, Newberry, 1856, Proc. Acad. 

 Nat. Sci., vol. 8, p. 96, Coal Meas. 



granulata, Newberry, 1856, Proc. Acad. 

 Nat, Sci., vol. 8, p. 97, Coal Meas. 



insculpta, Newberry, 1856, Proc. Acad. 

 Nat. Sci., vol. 8, p. 97, Coal Meas. 



lineata, Newberry, 1856, Proc. Acad. 

 Nat. Sci., vol. 8, p. 97, Coal Meas. 



ornatissima, Newberry, 1856, Proc. Acad. 

 Nat. Sci., vol. 8, p. 97, Coal Meas. 



ovoidea, Newberry, 1856, Proc. Acad. 

 Nat. Sci., vol. 8, p. 97, Coal Meas. 



serrata, Newberry, 1856, Proc. Acad. 

 Nat. Sci., vol. 8, p. 97, Coal Meas. 



tuberculata, Newberry, 1856, Proc. Acad. 



Nat. Sci., vol. 8, p. 96, Coal Meas. 

 MESODMODUS, St. John & Worthen, 1875, 

 Geo. Sur. 111., vol. 6, p. 290. [Ety. 

 mesodme, something between ; odous, 

 tooth.] Teeth laterally elongated ; base 



consisting of one inferior flattened; 

 posterior obliquely produced, massive 

 plate, of which the posterior face slopes 

 downward and slightly backward, at an 

 obtuse angle, to the posterior crown 

 face; anterior face slightly produced 

 along the shoulder, which extends par- 

 allel with the base of the crown, ver- 

 tical or beveled, and occupied by a 

 more or less prominent median pro- 

 tuberance, which extends to the edge 

 of the inferior surfaces ; both faces are 

 more or less roughened or pitted, lat- 

 eral angles truncated or rounded, and 

 more or less constricted above, equal- 

 ing the lateral diameter of the crown ; 

 crown rising along the anterior border, 

 sharply constricted in front and later- 

 ally, and well defined, sometimes con- 

 stricted from the posterior basal face, 

 nearly equaling the base in antero- 

 posterior diameter; but more or less 

 compressed along the crest, which rises 

 into a more or less prominent median 

 or submedian cusp, vertical or laterally 

 deflected and recurved, usually com- 

 pressed, with distinct, sometimes sharp, 

 cutting edges; the lateral portions of 

 the crown denticulated, extremities 

 bearing slightly more prominent cusps 

 than intermediate spaces; both faces 

 ridged vertically ; outer face of median 

 cone often strongly buttressed ; coronal 

 surface enameled. Type M. exculp- 

 tus. 



explanatus, St. John & Worthen, 1875, 

 Geo. Sur. 111., vol. 6, p. 293, Waverly or 

 Kinderhook Gr. 



exculptus, St. John 

 & Worthen, 1875, 

 Geo. Sur. III., vol. 



verfy o?kind> e - ll 7 P 'Z mod ' li 

 hook Gr. 



ornatus, St. John & Worthen, 1875, 

 Geo. Sur. 111., vol. 6, p. 294, Burling- 

 ton Gr. 



MYCTEROPS, Cope, 1888, Am. Nat., p. 876. 

 [Ety. mukter, nose ; ops, eye.] Founded 

 upon the cast of the cranial and nuchal 

 buckler of a placoderm fish ; the eye- 

 holes resemble those of Cephalaspis, 

 and they are separated by a nose-hole, 

 which is divided by a narrow bridge. 

 Type M. ordinata. 



ordinata, Cope, 1888, Am. Nat., p. 876, 

 Coal Meas. 



Onchus, Agassiz, 1837, Recherches sur lea 

 Poissons Fossiles. [Ety. onchos, bent, or 

 hooked like a talon or arrow-barb.] 

 deweyi, see Ceratiocaris deweyi. 



ONYCHODUS, Newberry, 1857, Bull. Nat. 

 Inst, p. 5, and Ohio Pal., vol. 1, p. 

 296. [Ety. onyx, a claw; odous, tooth.] 

 Cranium composed of a great number 

 of plates covered with an enameled 

 and tuberculated surface ; jaws set with 

 numerous conical, acute, recurved 

 teeth; maxillary forming a low trian- 



