84 DESMIDS OF THE UNITED STATES. 



C. LATUM, Breb. Plate XVI, fig. 14. 



Large, slightly longer than broad : constriction deep, 

 sinuses narro^v, somewhat enlarged within ; semi-cells broad 

 reniform, sides rounded, and back (dorsum) broad, rather 

 flatly rounded, margins dentate- crenulate ; cytioderm cov- 

 ered with pearly granules which are disposed in curved, 

 concentric series. 



Diameter about 60 ^. 



Bears a resemblance to C. margca-itiferum, but it is some- 

 what larger ; and according to Brebisson, more flatly rounded 

 in the middle, and base more reniform. Find it rather rarely 

 intermingled with other forms, and sometimes question the 

 characters for a good species. 



C. EENIFOEME, (Ealfs), Arch. Plate XVII, figs. 10, 11. 



A diagnosis of this species would not differ from the last, 

 C latum, except in the size of pearly granules, which are 

 nearly twice as large, (well shown in the empty cell fig. 11) 

 and in the more decided reniform figure of the semi-cells. 



The only habitat hitherto found for this form is a pond in 

 Florida; collected bj' J. Dounell Smith, of Baltimore, Md., 

 1879. 



C. OCHTHODES, Xord. Plate XVII, figs. 3, 4. 



Cells one and one-half times longer than broad, somewhat 

 elliptic-oblong, deeplj' constricted, sinuses narrow linear ; 

 semi-cells semicircular or subtriangular, sides convex ; apices 

 truncately rounded, or frequently slightly refuse in center ; 

 margins densely crenated ; viewed from the vertex, ellii)tic, 

 from the side, obovate. Membrane densely verrucose, ver- 

 rucae large, depressed, arranged in subregular or concentric 

 series. 



Diameter 52-70 yU. 



Hitherto have found this variety only in eastern Pennsyl- 

 vania. The original of the species was found in northern 

 Sweden, and described by O. Nordstedt ; it bears the resem- 

 blance to C. Botrytis, and C. tetrophthalmum, but differs in 

 the form of the verrucae which are short cylindrical truncate; 

 in tetrophthalmum the verrucae are triangular hemispherical 

 obtuse, and in C. Botrytis triangular with subacute apices. 



C. PoETiANUM, Archer. Plate XVII, figs. 12-14. 



Cells about oue-third longer than broad, deeply constricted; 

 semi-cells oval, remote, separated by a wide sinusj; isthmus 

 about one-fourth the diameter of the cell, membrane granular. 



Diameter 25-33 yu. 



