OPI. ORT.] 



LAMELLIBRANCHIA TA. 



497 



narrow, bearing from one to four long, 

 slender, ridge-like teeth ; anterior plate 

 broad, marked by numerous, small, 

 point-like teeth, with intermediate de- 

 pressions, arranged somewhat radiating 

 from the middle of its inner border ; 

 adductor muscles two, one at each ex- 

 tremity ; pallial line entire ; ligament 

 internal. Type N. arguta. 



FIG. 871. Nyassa arguta. Left valve. 



arguta, Hall, 1870, Prelim. Notice Lam. 



Shells, p. 28, and Pal. N. Y., vol. 5, pi. 



53, figs. 9-20, Ham. Gr. 

 elliptica, Hall, 1870, Prelim. Notice. Lam. 



Shells, p. 30, and Pal. N. Y., vol. 5, pi. 



34, fig. 8, Up. Held. Gr. 



FIG. 872. Nyassa arguta. Interior of right valve. 



parva, Walcott, 1885, Monogr. U. S. Geo. 

 Sur., vol. 8, p. 173, Devonian. 



recta, Hall, 1870, Prelim. Notice Lam. 

 Shells, p. 29, and Pal. N. Y., vol. 5, pi. 

 53. figs. 1-8, Ham. Gr. 



subalata, Hall, 1870, Prelim. Notice Lam. 

 Shells, p. 29, and Pal. N. Y., vol. 5, pi. 

 53, figs. 21-26, Ham. Gr. 

 Opisthoplera, Meek. Not defined. 

 ORTHODESMA, Hall & Whitfield, 1875, Ohio 

 Pal., vol. 2, p. 93. [Ety. orthos, straight ; 

 desma, a ligament.] Elongated, ventri- 

 cose; cardinal line straight posterior 

 to the beaks, and contracted anterior ; 

 ligament external; posterior scar elon- 

 gate, anterior smaller; pallial line sim- 

 8le ; surface concentrically lined. Type 

 . rectum. 



byrnesi, S. A. Miller, 1881, Jour. Gin. Soc. 

 Nat. Hist., vol. 4, p. 76, Hud. Riv. Gr. 



contractual, Hall, 1847, (Orthonota con- 

 tracta,) Pal. N. Y., vol. 1, p. 300, Hud. 

 Riv. Gr. 



cuneiforme, S. A. Miller, 1880, Jour. Gin. 

 Poc. Nat. Hist., vol. 3, p. 314, Hud. 

 Riv. Gr. 



curvatum, Hall & Whitfield, 1875, Ohio 

 Pal., vol. 2, p. 95, Hud. Riv. Gr. 



faberi, n. sp. Shell large, posterior part 

 of the cardinal line very slightly ele- 

 vated, and anterior part contracted in 

 front of the beaks; anterior end 

 rounded, posterior end more abrupt ; 



baeal line contracted in the central 

 part by an undefined cincture arising 

 below the umbones; beaks anterior, 

 obtuse ; umbones low and poorly de- 

 fined ; shell unusually high and thin 

 for species in this genus; surface con- 

 centrically furrowed. This pperu-s bears 

 some resemblance to a Modiolopsis, but 

 it is doubtless an Orthodesma. Col- 

 lected by Mr. Charles Faber in the 

 upper part of the Hud. Riv. Gr., at 

 "ersaillts, Indiana. 



up 

 Ye 



mickelboroughi, Whitfield, 1878, Jour. 



Cin. Soc. Nat. Hist., vol. 1, p, 139, Hud. 



Riv. Gr. 

 occidentale, S. A. Miller, 1880, Jour. Cin. 



Soc. Nat. Hist., vol. 3, p. 316, Hud. 



Riv. Gr. 

 parallel um, Hall, 1847, (Modiolopsis 



parallela,) Pal. N. Y., vol. 1, p. 158, 



Hud. Riv. Gr. 

 rectum, Hall & Whitfield, 1875, Ohio 



Pal., vol. 2, p. 94, Hud. Riv. Gr. 



FIG. 874. Orthodesma rectum. 



subovale, Ulrich, 1879, Jour. Cin. Soc. 

 Nat. Hist., vol. 2, p. 82, Hud. Riv. Gr. 

 OKTHONOTA, Conrad, 1841, Ann. Rep. 

 N. Y., p. 50. [Ety. orthos, straight; 

 notos, the back.] Transversely elon- 

 gate ; margins subparallel ; cardinal 

 line straight ; two cardinal teeth ; no 

 lateral teeth; ligament external; um- 

 bonal ridge oblique. Type 0. undulata. 



angulifera, (?) McCoy, 1850, Brit. Pal. 

 Rocks, p. 276, Up. BEL 



carinata, Conrad, 1841, Ann. Rep. N. Y., 

 p. 5t, and Pal. N. Y., vol. 5, pi. 78, figs. 

 34-35, Ham. Gr. 



contracta, see Orthodesma contract am. 



curta, Hall, 1843, Geo. Rep. 4th Dist 

 N. Y., p. 76, and Pal. N. Y., vol. 2, p. 

 86, Clinton and Niagara Gr. 



ensiformis, Hall, 1870, Prelim. Notice 

 Lam. Shells, p. 89, and Pal. N. Y., vol. 

 5, pi. 78, fig. 36, Ham. Gr. 



incerta, Billings, 1874, Pal. Foss., vol. 2, 

 p. 130, Up. Sil. 



parallela, see Orthodesma parallelum. 



