190 MYTILIDiE. 



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

 however, we find the lower mai-gin 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 ai)pear 

 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 tln-ough horn 

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

 modes and in vai'ious proportions. What Mr. Conrad regards as a 

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

 ing more than a variety of this shell. 



Ocmis MODIOLARIA, Gray. 1842. 



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

 strite, whicli 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, incurrcnt tube, 

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



Modiolaria nigra. 



Fig. 86. 



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

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

 radiating lines. 



Miftlhui (lisrors (var.), Chemn. Conch, viii. 195, pi. 86, fig. 767. — Schrot. Einleit. iii. pi. 



9, fis:. 15. — O. Fabu. (var. suecints), Danske Vidcnsk. 1788, 460. 

 Myt'dm discrepans, Montagu, Test. Suppl. 65, pi. 26, fig. 4. — Wood, Ind. Test. pi. 12, 



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



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



Fauna, 164. 

 Modlola discrppana, Flem. Br. An. 413. — Brom'n, 111. 78, pi. 27, fig. 8. — Sowerhy, 



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



1844, 102. 

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



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

 Modioki deprcssn, Hanley, Recent Shells, i. 242, note. 

 Modiola nem, Goui.D, Inv. 1st cd. 128, fig. 86. — Mighet.s, Shells of Maine, Journ. 



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

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



pi. 44J fig. 5 ; pi, Q (anim.ll). — Gray, Cat. Br. Mcll. pi. 7, 121. 



