MOPAMA. 



turnl with plumr-likr radii, granose at the SUtun -, t h.- ii;iL r "iial ribs 



and tin- radiating rililrts of the head-valve ; the grains elongated, 

 siihspinose, elegantly strrntimj (fie sutures. 



Interior pule blue. Tail valve having the p.~t< Ti-.r linoi hardly 

 indicated externally, xinof/, //'// <t minute toof/i 00J /// nf //: apex; 

 at one title it fut* "2, <it ike other 3 slits; slit-rays Inconspicuous. 

 Central valves having 1, anterior valve 8 slits, the slit-rays con- 

 spicuous; teeth acute, small. Eaves small, very spongy. Sinua 

 s-iuall, deep, flat, the sutural plates separated. 



Girdle thin, narrow, smooth, sparsely and irregularly beset with 

 subtranslucent, larger and smaller tubular bristles. 



Length 16i, width 11 mill. ; divergence 112. 



Habitat unknown. 



The above description, from Carpenter's MS., was drawn from a 

 single specimen in the collection of Dr. Wesley Newcomb (now of 

 Cornell College). The figures 80, 81 represent the same specimen. 



V&r.fissa Cpr. Sculpture between that of M. acuta and M. pin- 

 mosa ; the granules at the suture and diagonal rib hardly claw- 

 shaped; color and form also intermediate. Interior: posterior 

 valve having two slits on one side, one on the other, the median 

 caudal sinus minute, acutely slit ; otherwise normal. Girdle smooth 

 with sparse, small spines. 



Length 15, breath 10 mill. ; divergence 115. 



This form was described by Carpenter from a single specimen 

 from Monterey. It differs from acuta and plumosa in lacking the 

 "key-stone" like structure of the caudal sinus; but the series 

 examined by me proves that this character has no constancy. 



Subspecies M. LIGNOSA Gould. PL 63, figs. 58, 59 (typical) ; 60, 

 61, 62, 63. 



Shell oval, elevated, carinated or angular at the dorsal ridge, the 

 side-slopes straight. Surface lusterless, apparently smooth ; grayish, 

 greenish or bluish with radiating streaks, lines and flammules of 

 brown or purple-brown. 



Under a lens the lateral areas appear nearly smooth ; the central 

 areas being closely and finely pitted all over. Girdle narrow, 

 sparsely hairy. 



Interior white and light blue. Length 60, breadth 35 mill. ; 

 divergence 120. 



Vancouver I. to Monterey, California. 



