754 



SYSTEMATIC HISTOEY OF THE INFUSORIA. 



S. duplex (Ealfs). — Cells two, slender, 

 tapering, skpnoid, acute, ^j/«re(^Z side hy 

 side for about half their lencjtli. = Rhaphi- 

 dium duplex (Kg.), nee S. 7noniliformis 



(duplex) (Kg.). G.B., CI. This plant 

 possibly represents a cell of an Ankis- 

 trodesmus during division. 



Genus PEDIASTHUM (Meyen). — Frond or family plane, circular, elliptic, 

 or irregular, composed of several cells (a multiple of four), forming by their 

 union a flattened star-like group, generally arranged in more or less con- 

 centric circular series, marginal cells externally bipartite or entire ; propa- 

 gating by '' macrogonidia," which are subgiobose, formed by repeated binary 

 division of the endochrome of each of the parent-cells of the old frond, 2, 4, 

 8, 16, 32, or G4 (even 128) in number, and making theii' exit by a transverse 

 fissure from the parent-ceU, involved in its inner membrane, mthin which 

 for a time they actively move, presently settling down and arranging them- 

 selves into a new frond ; '" microgonidia " produced in the same manner, but 

 shortly rupturing the confining membrane and swimming freely away, their 

 fate unkno^\^l (Braim). 



* Lohes of the outer cells two, deeply 

 emarginate or truncate. 



Pediasthum Tetras (Ralfs). — Frond 

 very minute ; cells four, their interstices 

 forming a ci'oss, their outer margin bi- 

 "lobed, angles acute. L. 1-2941" ; B. 

 1-2272". (ii. 27.) = Micrasterias Tetras 

 (Ehr.), P. biradiatum (Tetras) (Kg.). 

 G.B., I., F., G., U.S.A. 



P. heptactis (Menegh.). — ^Frond minute; 

 cells eight (seven disposed in a single series 

 round a central one), bilobed, angular. 

 L. 1-2900" ; B. 1-2500". = Micrasterias 

 heptactis (Elir.), Euastnmi hexagonum 

 (Corda), P. simplex (Hass.), P. hira- 

 diatum (heptactis) (Kg.). G.B., I., F., 

 G., U.S.A. 



P. biradiatum (Menegh.). — Inner cells 

 subcpiadrilateral, with a linear notch, the 

 outer quadrilateral or somewhat cuneate, 

 approximate for their entire length, ex- 

 ternally deeply bipartite, their incisions 

 narrow, the subdivisions truncate or 

 truncate - emarginate. L. 1-1200" to 

 1-2650" ; B. 1-1754" to 1-2040;'. = Mi- 

 crasterias Rotida (Ehr.), P. biradiatum 

 (Rotula) (Kg.). This with the two pre- 

 ceding may possibly make but one true 

 species, P. Elirenberqii (Braun.). (i. 52.) 

 G.B., I., F., G., U.S.A. 



P. Rotula (Ehr. emend. Braun). — 

 Inner cells with a tcide notch, and sepa- 

 rated by wide lacunae, the outer subqua- 

 drilateral, approximate only at their bases, 

 tchich are nearly square, externally deeply 

 bipartite, their incisions broad, the sub- 

 divisions naiTow, inciso-dentate. F., G. 



P. caudatum (Braun). — Inner cells 

 pentagonal or hexagonal, with a deep 

 linear notch, the outer quadrangidar, 

 externally deeply bipartite, the subdivi- 



sions truncate, very slightly concave at 

 the centre, aiul furnished at the angles ivith 

 a very minute, shorty bristle-like spine. 

 = P. Rotula (Nag.). G. 



2 * Lobes of the outer cells two, entire, 

 attenuated. 



P. Selencea (Kg.). — Cells crescent- 

 shaped, arranged in one or more circles 

 round one or two central ones, connecting 

 mediinn coloured. = P. elegans (Hass.), 

 P. lunare (Hass.). G.B., F., G. 



P. gracile (Braun). — Frond minute, 

 of fom- or six cells (fom* external, Vvdth 

 or without two central cells) ; marginal 

 cells deeply bipartite ; subdivisions ovate, 

 tapering to a point. L. 1-1020" ; B. 

 Y-Vo^'i" .■= Micrasterias Coromda (Ehr.), 

 P. Napoleonis (Hass., Menegh., Kg., nee 

 Ralfs), P. simptex (Ralfs). G.B., F., G. 



P. pertusum (Kg.). — Cells aiTanged 

 in circles round one or two central ones ; 

 inner cells quadrangidar, sides concave 

 and leaving angular vacant intervals ; the 

 outer cells tcith square bases, externally 

 triangidarly notched, the subdivisions ta- 

 pering to an acute point. L. 1-2266" ; 

 B. 1-3268". = Micrasterias Boryana 

 (Ehr.), P. tricyclium (Hass.), P. emargi- 

 natuni (pertusum) (Kg.). G.B., I., F., G. 



P. granidatum (Kg.). — Cells eight, 

 rough loith minute granules, six cells 

 arranged round two central, the inner 

 subquadrate, the outer ha\-ing two taper- 

 ing lobes. L. 1-2000"; B. 1-1850". 

 G.B., I., F., G. 



P. A^fl;;o/eo«is (Menegh.).— CeUs eight, 

 six an-anged roimd two centi-al, the inner 

 variable, the outer having two cuspidate 

 lobes, the notch wide. (i. 62.) L. 1-1570" 

 to 1-1483" ; B. 1-1813" to 1-1088". = P. 

 hexactis (Hass.). G.B., G. 



