351< WILLtAM ARCHER. 



incisuris quaternis in cellulas iilias quaternas dilapsa, cellulse 

 filise post divisionem individuas singulas se proebentes, inci- 

 surarum directio in marginum lateralium directione perpen- 

 diculari aut in angulo semirectangulo versa ; cellularum in 

 teranea granulosa, colore eerugino. 



Tetrapedia gjothtca. P. Reinsch. 



Celkilte in sciagraphia quadraticse, margines laterales in 

 medio non profunda incisi, lobulo in medio paulo emarginati ; 

 cellulse evolutiores quadripartitse, incisurarum directio in 

 marginum lateralium directione perpendicularis. (PI. XXI, 

 figs. 1 to 7.) 



Latit. 0*006 mm. usque 0"008 mm. ; familise ex quaternis 

 cellulis extnictee latit. 0"013 mm.; familise ex cellulis 16is 

 extructae latit. 0'027 mm. usque 0*03 mm. 



Tetrapedia Crux Michaeli. P. Reinsch. 



Cellulae in sciagraphia quadraticse, margines laterales in- 

 tegerrimi utrimque leniter emarginati ; cellulse evolutiores 

 (in statu divisionis) quadripartitse, incisurarum directio in 

 marginum lateralium directione angulo semirectangulo versa. 

 (Figs. 9 to 10.) 



Cellularum (in statu divisionis) latitudo 0"008 mm. usque 

 0-012 mm. 



The first species [T. gothica), I have never had the good 

 fortune to encounter, and would, indeed, be extremely glad 

 to have an opportunity to examine so remarkable a unicellu- 

 lar growth. As is seen from the figure (PI. XXI), a young 

 cell in T. gothica is compressed, quadrate, slightly emarginafe 

 at the middle of each lateral margin, the angles rounded, a 

 slight marginal concavity between each of the four central 

 emarginations and each of the four angles (figs. 1, 2) ; side- 

 view oblong, concave at the middle at each side, and broadly 

 rounded (fig. 7). By-and-by, as would appear, the cell be- 

 comes more and more deeply incised at all the four sides, the 

 incisions, taking origin equi-distantly from the angles — that 

 is to say, from each of the four lateral emarginations, of 

 which, indeed, these are but the initiations — proceed in a 

 direction perpendicular to the sides, until they almost reach 

 the centre (figs. 4, 5). The cell is now cut very nearly into 

 four quadrate qviarters,but these remain still mutually attached 

 by a narrow connecting portion, and, of course, this forms a 

 bond of union, and must maintain a passage of intercommu- 

 nication between the cavities of the four quadrate sections ; 

 this, at least, is very plainly conveyed by Reinsch's figure. 

 Pari passu Avith the progress of these lateral and vertical in- 



