458 DESCEiPTiON OF [^Polygastrica. 



represent the seminal gland of Ehrenberg. Self-division longi- 

 tudinal and ventral; the parts dividing themselves before the 

 restoration of the original form, which, indeed, in some specimens, 

 is never restored, the portions remaining like bows, or semi-lunar- 

 shaped pieces. After division both the halves gape, and take an 

 apparently oblique position in regard to the stalk ; those bodies which 

 are separated from their stalks have a free movement. 



Kiitzing thus characterizes the genus Cocconema, as one of the 

 family Cynibellecs, — " Individuals solitary or geminate (in pairs), 

 stallced; in other respects like CymhellaP 



From Ejnthemia it differs in having a central umbilicus ; from 

 Amphora and Navicula, by its asymmetrical form; and from all 

 three, also, by being stalked. From the allied stipitate genus 

 Gowi/plionema, the central umbilicus constitutes the mark of 

 distinction. 



The individuals are probably solitary and free in the earliest stage, 

 the stipes being a subsequent development. 



Besides propagating by fission, the members of this genus are 

 known to exhibit the process of conjugation. The latter has been 

 watched by Mr. Thwaites in C. lanceolatum, and, unlike what mostly 

 occurs, the developed, sporangial bodies, have a close resemblance to 

 the original frustules, the chief difference being in their larger size. 



Most species of Cocconema are of fresh-water habit ; several have 

 been foimd fossil. 



Cocconema ^oetM. — Large, lanceolate, subacute at the extremities, 

 striated, and attached to a branched pedicle. Ehrenberg states he 

 has not seen a central opening, but that there is one near each end on 

 the ventral aspect. Found in sea-water, j!^orth Sea and Baltic. 

 Striae twenty-six in l-1200th. Length l-430th. to l-210th. 



C. lanceolatum. — Semi-lanceolate, closely striated ; ends obtuse, 

 attached to 'a dichotomously branched pedicle, ia which it differs 

 from Eunotia turgida, as also ia the presence of a central opening in 

 theloi-ica. (P. 4, f. 194, 195.) Length l-210th. to l-120th. 



C. cistula. — Small, semi-ovate, obtuse, striated ; pedicle long, 

 simple, and sometimes branched ; central openings distinct, terminal 

 ones obscure. Free specimens resemble Eunotia fala ; the young are 



