Naviculacea.'] infusorial ANiMALcrLES. 3U 



Pijxidicula Coscinodiscus, of Virginia, -would seem to be a member 

 of this genus. 



CKAsrEDODiscus elfigatis. — Disc large, central cells radiant, seven in 

 l-1200th; five to six larger oblong ones constitute a centi'al umbilicus; 

 margin tumid, l-llo2nd wide, with larger obliquely quadrate cells, 

 six in l-1200th. Diameter l-132nd. Bermuda (P. 14, f. 38.) 



C. Coscinodiscus = Pijxidicula Coscinodiscus. — Central cells of the 

 disc small, decreasing towards the centre, seventeen to eighteen in 

 1-1 200th; no umbilical star; cells of the margin larger, unequal, 

 hexagonal, about ten to eleven in 1-1 200th. Diameter l-39Gth. 

 Richmond, Virginia. The rim of this species is wider than that of 

 the preceding. 



Genus Cxclotella (Kiitz.) — Individuals solitaiy or binate, disci- 

 form, orbicular ; the primary side distinct, forming a ring ; the 

 secondarj'- plane. Lorica bivalve, valves plane, orbicular, conjoined 

 by an interstitial ring. 



Sect. I. Individuals included in an amorphous gelatinous suhstance, 

 (Discoplea, Ehr.) 



C. operculata = Discoplea Kutzingii (Ehr.) = Pyxidicula operculata. 

 Secondary sides dotted on the margin. Diameter l-1020th. Common 

 in fresh water. ■** 



C. Meneghiniana. — Secondary sides striated on the margin. 

 Diameter l-1440th. Berlin. 



Sect. II. Individuals adnate (free.) 



C. Scotica. — Small, quite smooth. Diameter of the plane disc 

 l-960th. On Conferva, Coast of Scotland (P. 17, f. 17.) 



C. ligustica. — Of middling size, quite smooth, adnate or free. 

 Diameter of plane disc 1 -720th to 1 -51 6 th. On filiform AlgaB, Genoa. 



C. maxima. — Large, minutely pimctate, adnate. Diameter of the 

 nearly plane disc l-300th to l-126th. On Polysiphonia, Coast of 

 Peru, Chili. 



C. (?) mimitula. — Small, with radiating and flexuosc striae on the 

 secondary side. Diameter 1-1 200th. Eossil in Lunebcrg. It may 

 be but a separated segment of Melosira. 



C. (?) Rotula — Rather small; secondary side with radiating striae, 

 and a dotted centi'e ; one side convex, the other concave. Diameter of 



