252 DESCEiPTioN OF [Poli/gastrica. 



Those species having cylmch-ical fronds, show an affinity with 

 Penium ; but in that genus the constriction is either wanting or 

 obscui'e, and the segments are longer than broad. Cosmarium is 

 always constricted in the middle, and the starch vesicles are scat- 

 tered. Tetmemorus differs in its elongated fronds and emarginate 

 extremities. 



1 . Frond comjjressed, deeply constricted at the middle ; end view ellipti- 

 cal. — Margin of segments entire. 



CosMAJRiUM quad/ratum. — Minute, smooth, deeply constricted ; seg- 

 ments in front view quadrate, and on each side of the base slightly 

 protuberant ; its ends less rounded than in C. cucumis. 



C. Cucumis = Euastrum integerrimum, Ehr. (?) — Smooth, deeply 

 constricted ; segments as broad as long, rounded at the ends ; trans- 

 verse view broadly elliptic ; smaller than C. JRalfsii, less orbicular, 

 and transverse view different. 



CosMAiiiXTM Ralfsii. — Large, orbicidar, smooth ; deeply constricted ; 

 transverse view fusiform. Differs from C. Cucumis by its larger size 

 and disciform appearance. Length 1 -225th. 



C. pyramidatum. — Oval, with flattened ends, deeply constricted ; 

 seg-ments punctate, entire. Frond about twice as long as broad, 

 varying much in size. Sporangia orbicular, and tuberculated. Dis- 

 tinguished by its puncta and depressed ends. 



C. tinctum. — Yery minute, smooth; constriction producing a 

 linear notch on each side ; segments elliptic ; integument reddish ; 

 sporangium naked, subquadrate, conjugating ft-onds persistent. Smaller 

 than C. hioculatum , and its notches less gaping. 



C. hioculatum. — Very small ; smootli ; constriction producing a 

 gaping notch on each side ; segments sub-elliptic, entii-e ; sporangium 

 orbicular, spinous. Differs from C. pliai^eolus in its smaller size, and 

 more elliptic segments, "svhich are not in apposition. 



C. deperessum (Bailey.) — Elliptical, binate, division in the plane of 

 the longest axis. Segments entire, nearly twice as long as broad. 

 Lakes in Florida. This species resembles C. hioculatum, (Brobisson.) 

 But the segments arc much closer together, and are angular, not 

 rounded at the basal extremities. 



C. granatum. — Constriction of fr-ond forming a linear notch on 

 each side ; segments compressed, smooth, truncato-triangular. Larger 

 than C. hioculatum and C. Meneghinii. Length 1-123 1th. 



