190 MYTILID^. 



This species seems to be subject to little variety. Sometimes, 

 however, we find the lower margin nearly straight. In this case the 

 upper margin is nearly parallel to the lower, so that the shell in- 

 creases but little in height ; and in such shells the beaks appear 

 much more prominent than in ordinary specimens. 



The principal variations seem to consist in the coloring, which is 

 made up of various shades, from bright yellow, passing through horn 

 color and chestnut to dark bronze-green, and arranged in various 

 modes and in various proportions. What Mr. Conrad regards as a 

 distinct species, under the name semi-costala, certainly can be noth- 

 ing more than a variety of this shell. 



Ociliis inODIOLARIA, Gray. 1842. 



Shell rhomboidal, sculptured by two rows (one on each side) of 

 striae, which radiate from the beaks, leaving the middle portion 

 smooth ; beaks incurved ; hinge mostly toothless, but sometimes 

 crenulated ; hinge-plate finely notched. 



Body sub-oval ; mantle folded in front into a wide, incurrent tube, 

 and behind into a conical, excurrent tube ; foot strap-shaped. 



Modiolaria nigra. 



Fig. 86. 



Shell ovate, ferruginoiis, beaks prominent, and placed considerably behind the 

 anterior extremity ; minutely reticulated with fine, corrugated, concentric, and 

 radiatins: lines. 



o 



li/ijtilus discors (var.), Chemn. Conch, viii. 195, pi. 86, fig. 7G7. — Schrot. Einleit. ill. pi. 



9, fiir. 15. — 0. Fabr. (var. suecir.us), Danske Vidensk. 1788, 4G0. 

 Mijtilus discrepans, Montagu, Test. Suppl. 65, pi. 26, fig. 4. — Wood, Ind. Test. pi. 12, 



fig. 38. — Leach, Zool. Misc. ii. 36; Append. Koss's Voy. 176. — Maton and 



Rackett, Lin. Trans, viii. Ill, pi. 3, fig. 9. — Tlrtox, Conch. Diet. 112; Br. 



Fauna, 164. 

 Modiola discrepans, Flem. Br. An. 413. — Bro-nvn, III. 78, pi. 27, fig. 8. — Soweruy, 



Gen. Shells (Mod.), fig. 3. — Reeve, Conch. Sys. pi. 100, fig. 3. — Phil. Zcitbch. 



1844, 102. 

 Modiola nigra. Gray, Append. Parry's Voy. 244 (adult) (1824). — Thorpe, Mar. Conch. 



249, fig 2 (jun.). — Hanley, Recent Shells, i. 242, pi. 12, fig. 38. 

 Jlfodioln deprcssa, Hanley, Recent Shells, i. 242, note. 

 Modiola nexn, Gocld, Inv. 1st ed. 128, fig. 86. — Mighels, Shells of Maine, Journ. 



Bost. Soc. iv. 327. — Reeve, Elem. Conch, ii. 73, fig. 173. 

 Crenella nigra. King, Ann. Nat. Hist, xviii. 239. — Forbes and Hanl. Br. Moll. ii. 202, 



pi. 44, fig. 5 ; pi. Q (animal). — Gray, Cat. Br. MlII. pi. 7, 121. 



