194 MYTILID^. 



anterior compartment : those in the posterior compartment are more 

 crowded, more distinct, the intervening spaces rounded ; and when 

 viewed under the microscope, the whole surface is found to he cov- 

 ered with minute wrinkles of the epidermis crossing the ribs and 

 the spaces between them, and also the middle compartment ; epider- 

 mis greenish-yellow with clouds of olive. Within silvery, margin 

 crenulated by the ribs, and with three or four teeth before the beaks. 

 Eastport to Cape Cod (^Stimpson) ; Greenland (^Miiller^ ; Sambro 

 Bend and Sable Island (^Willis^. 



Oeniis CRENELL.A, Brown. 1827. 



Shell oval or rhomboidal, cancellated by longitudinal ribs and 

 transverse plates ; beaks straight ; ligament small ; hinge of each 

 valve furnished with an upright tooth, which is crenulated as well 

 as the hinge-plate. 



Body roundish-oval ; mantle open in front, and folded behind into 

 a sessile excurrent tube ; foot worm-shaped, the point being disk- 

 like and issuing out of a sheath. 



Crenella glandula. 



Fig. 87. 



Shell obliquely rounded-oval, regularly convex ; beaks small, separate ; sur- 

 face with minute lines of growth, crossed by minute and crowded radiating lines; 

 epidermis brownish-yellow ; margin crenulated. 



Modiola glandula, Totten, Silliman's Journ. xxvi. 367, figs. 3, e, /, g. — Gould, Tnv. 



131, fig. 87. 

 Afi/iilm clecussatus, Stimpson, Shells of New England, 11. 



('renfilla dermmta, Forbes and Hanl. — Di-; K.vy, N. Y. Moll. 186, pi. 22, fig. 248. ; 



Crenella glandula, Stimpson, Smith. Inst. Check Lists (1860), 2. I 



Shell small, thin, rounded -oval, rather inflated, convexity regular; 



beaks small, rather prominent, curving, not in contact, placed at ' 



about half the height of the shell ; anterior portion ' 



^^^^^ slightly depending, base nearly straight, and the rest of 



the margin regularly rounded ; surface with minute lines 



of growth, crossed by very small, rounded, radiating 



c. glandula ^'^^^^' al)out cqual in size on all parts of the shell, the 



number increasing as the spaces between them widen ; 



epidermis thin, brownish-yellow; within white, somewhat pearly; 



edges sharp and minutely crenulated, except the short portion occu- 



