418 DEScEiPTioN OF [PoIj/ffasMca. 



obtusely truncate ; central umbilicus transverse, and divided by a 

 longitudinal line into two parts. Mexico. 



PrNNULARiA disphenia. — Striated, linear, elongated dorsally, sides 

 straight ; ends acutely wedge-shaped ; pinnules of margin veiy 

 minute ; ai^proaches P. ampMgomphus. 



P. Entomon. — Larger, elongate, widely constricted at centre, 

 (panduriform) presenting two oblong portions with cuncate ex- 

 tremities, subacute ; striae smooth, not granular ; broad, nineteen to 

 twenty in 1-1 200th. Alive and fossil. 



P. Esox. — Large, elongate ; naiTowly lanceolate, dorsally, slightly 

 undulate on the sides ; three undulations on each side, of which the 

 central one is the most marked. Extremities very attenuate, but 

 obtuse. (P. 15, f. 43.) ChiH. 



P. Gastrum. — Striated, small ; underside widely lanceolate ; ends 

 constricted, but little produced, and obtuse, with granular eminences. 

 Mexico. 



P. Gigas. — Very large, wand-shaped, slightly gibbous at centre of 

 dorsum, gently diminishing towards extremities, which are rounded ; 

 nine pinnules (striae) in 1-1 200th; approaches Y.nohilis. North 

 America 



P. heteropleura. — Broadly lanceolate on the back ; sides unequal ; 

 ends slightly constricted and broadly obtuse. Is near P. inmqualis, 

 the ends of which are however sub-acute. 



P. isocephala. — Linear on back, undulate, with five eminences 

 (nodules) produced by as many constrictions, somewhat of unequal 

 size ; whence it has a moniliform outline. Scarcely differs from P. 

 Monile which is larger. 



P. macilenta, — EaciUar dorsally ; sides straight ; ends rounded, 

 wide ; pinnules nan-ower and closer than in preceding, there being 

 eighteen to twenty in 1-1 200th. This species = P. pohjptera, which 

 is probably but a more slender variety. 



P. mcesogongyla. — Striated, styliform, and bacillar ; gibbous at the 

 middle dorsally ; ends rounded, wide, not turgid ; near P. nohilis. 



p. monile. — Very small ; striated dorsally, constricted so as to form 

 five equal siib-globose segments ; viewed on the sides, it is linear 

 and truncate. Approaches Navicula nodom, Length l-864th. 



