246 DESCRIPTION OF [Polt/c/astrica. 



* * * * Fronds ohlony. 



MicEASTEKiAs Jemieri. — Oblong, minutely granulated; segments 

 five-lobed ; lobes closely approximate, cuneate ; lateral ones obscurely 

 bipartite, sub-divisions emarginate. Transverse view fusiform. {A.) 

 granules appearing like mere puncta ; (5) granules larger, giving a 

 dentate appearance to the margin. 



This species seems to unite Micrasterias with Euastrum. It 

 agrees with the latter genus in figiu-e, but the lobes have incon- 

 spicuous incisions, which divide them into two portions, each slightly 

 emargiaate. A transverse view shews the absence of the protuber- 

 ances always found ia true species oi Euastrum. Length 1-1 47th. 

 Breadth l-209th. 



* * * * * Loles horizontal, attenuated, hidentate. 



M. oscitans. — Smooth, with convex ends ; segments constricted ; 

 lobes horizontal, conical, bidentate. Transverse view fusiform. 

 Length l-156th. Breadth l-211th. (P. 13, f. 28, 29.) 

 >• M. pinnatifida. — Minute, plane, its ends straight ; segments deeply 

 constricted ; lobes horizontal, triangular, bidentate ; resembles If. 

 oscitans in foim, but its surface is flatter, the end margin straight 

 or slightly concave instead of convex, and the lobes more tapering. 

 Length 1 -440th. Breadth 1 -392nd. 



M. apiciilata = Euastrum apiculatum, (Ehr.) — Orbicular, rough, 

 "with scattered spines ; segments five-lobed, lobes incised and toothed, 

 and lobe narrow. 



M. quadragies-cuspidata. — Has scattered hair-like spines ; end lobe 

 the broadest. 



"M.. foUacea (BaUey). — Sub-quadrate; end lobes nan-ow, with 

 emargiaate angles ; lateral lobes inciso - dentate, with a short, 

 rounded tooth-like projection next the end lobe. 



M. Torreyi. (Bailey.) — Orbicular ; lateral lobes deeply incised ; 

 inner sub-divisions acute ; external, bidentate at the apex ; all taper- 

 ing. End lobe nan-ow and not exserted. 



M. muricata- — Segments divided by deep indentations into three 

 transverse portions ; the basal with three, the others with two linear 

 processes on each side. 



M. muricata differs remarkably from 31. furcata and eveiy other 

 known species. The division into five lobes is indicated merely 



