FAMILY MYTILIDiE — MODIOLA. 185 



MODIOLA MODIOLUS. 

 PLATE XXIV. FIG. S57. 



(STATE COLLECTION.) 



Mytilus modiolus. LiNN. Syst. Nat. 1158. 



Modiuta papuana. Lam. An. sans vert. Vol. 3, p. 11, Ed. Brux. 



M. id. Say, Am. Conch, pi. 45, Theton, Conch. Ins. Brit. pi. 15, fig. 3 (Young). 



M. modiolus. Gould, Invertebrata of Mass. p. 123. 



Description. Shell large, coarse and solid, oblong, obliquely dilated. Beaks tumid, ob- 

 tusely angulated, placed on one side, and nearly approaching the anterior margin. Basal 

 margin concave, with a fissure for the byssus. Surface coarsely marked with deep incre- 

 mental lines ; the groove for the ligament deep and elongated. 



Color. Epidermis thick and folded within the margins, dark violaceous approaching to 

 black, occasionally chesnut brown ; lighter along the ridge from the beaks ; within, pearly. 



Longest axis, 4*5 — 6*0 ; shortest, 2' 5 - 3"0. 



This species occurs in deep water along the whole coast, and is usually found after heavy 

 storms. It is subject to many variations in form, which have given rise, according to Dr. 

 Gould, to several nominal species, such as M. umhilicatus, harbatus, and gibhsii. The true 

 M. papuana, with which this has been confounded, as its name would seem to imply, is an 

 East-Indian shell : the animal is dark orange or reddish. 



(EXTRALIMITAL.) 



M. pectinula. (Gould, Invertebrata of Mass. p. 127, fig. 85.) Shell obovate, ventricose, -with about forty 

 equal radiating ribs ; beaks prominent, projecting as far as the anterior margin ; entire margin cre- 

 nulated by the ribs. Color: epidermis brownish yellow. Longest diameter, 0-7; shortest, 0'3. 

 St. George's Bank. 



M. nexa. (Id. lb. fig. 86.) Shell ovate: beaks prominent, and placed considerably behind the ante- 

 rior extremity, minutely reticulated with fine corrugated concentric and radiating lines ; front of the 

 beaks radiated. Color: epidermis rusty brown with shades of olive, glossy. Length, 0-7; short- 

 est axis, 0*4. Provincctown, Mass. 



M. (iiscrcfiaras, Montagu. (Gould, lb. p. 129, fig. 83.) Shell suboval, broadest behind : beaks nearly 

 terminal ; hinder extremity somewhat lobed. Surface divided into three compartments, of wliich 

 the anterior is marked by about eight, and the posterior by numerous radiating lines. Color : epi- 

 dermis oHve-green. Length, 1 -0; breadth, 0- 4. Stomachs of fishes. Coast of Massachusetts. 



M. discors, Montagu. (Gould, lb. p. 130, fig. 84.) Shell oval, tumid: upper edge somewhat com- 

 pressed and arching; posterior tip somewhat produced and pointed. Beaks large, nearly terminal: 

 surface with about sixteen ribs at the anterior third, and very numerous ones at the posterior third ■ 

 three or four teeth before the beaks. Color : epidermis greenish yellow, with clouds of olive. 

 Length, 1 -5; height, 0-3. Adhering to seaweed. Coast of Massachusetts. 

 Fauna — Part 6. 24 



