Naviculacea.'] infusoiual animalcules. 413 



Navicula {^) jniradoxa. — Large, quite smooth, widely obloug- ou 

 back ; slightly constricted at the middle ; ends cuneate, obtuse ; 

 centre longitudinally dotted. Pern. 



N. Ehomhea. — "VVidoly lanceolate on back, almost rhomboidal, -^dth 

 delicate longitudinal lines; ends acute. Length 1 -480th to 1 -360th. 

 Mexico. 



N. Semen. — Back ovate, turgid, ventricose at the centre, obtusely 

 rounded at the ends. Variety (</.) Ends rather constricted — N. 

 Chilensis. Var. {h.) Ends rounded — IS". Lahrador. 



JST. Silicula. — Smooth, linear, elongate, with three equal protube- 

 rances (nodes) on back ; one at the centre, and one at either end, 

 hence the ends obtuse. North America. 



N. Sphocrophora. — Lanceolate, ends produced (rostrate), capitate 

 and papillate. Length 1 -320th. In fresh water. 



N. Trabecula. — Linear, elongate, ^ith a single node at the centre, 

 ends not contracted, and round. Kiitziug thinks it to be a variety 

 of Pinnularia decurrens. 



N. nodosa. — Small, broadly oblong on back, sides with three equal 

 swellings; ends constricted, obtuse. Approaches N. Ilitchcockii. North 

 America. 



N. (?) omphalia. — Large, with gi-anulai- lines, which, from being 

 very finely decussated, reflect various colours ; umbilicus solid, 

 round, clear, with the median suture passing through it. A Iju-ge 

 and elegant species. Fragments from Bermuda, l-192nd in size. 



N. elliptioa. — Elliptic; ends imperfectly subacute; central uni- 

 biliary, subquadi-ate ; three fine sutures ; margin wide, very minutely 

 dotted. Length 1-5 76th. Southern Ocean. 



N. Cantonensis. — Broadly ovate, lanceolate, very smooth ; ends 

 acute, little produced. By its shorter acute ends it differs fi-om 

 l^.fuka. Length l-480th. Canton, China. 



N. Sinensis. — Flexuose, sigmoid, larger than preceding, very 

 smooth; ends widely rounded, expanded in the centre. Length 

 1-1 80th. 



N. tortuosa. — Bacillar, smooth, rather turgid, and tortuose. Length 

 1 -288th. 



N. decussata. — Oblong-eUiptic, strong, constricted at each end, as if 

 obtusely mucronate ; surface elegantly sculptured by decussatiu" 



