472 DESCEiPTioN ov [Poli/ffastrica. 



margin ; rhomboidal, club-shaped, and sliglitly pointed. In salt- 

 water. Length 1-1 40th. (P. 16, f. 14,) North Sea and Baltic. 



PoDosPHENiA (?) nmia. — The dwarf Podosphenia. — Smooth, linear, 

 cuneate ; laterally clavate, without striae. Length 1 -2300th to 

 1-1 720th. Fossil at Bilin. 



P. tergestina (Kutz.) — Cuneate, triangular; bacilli geminate (in 

 pairs), or tcrnate, conjoined in a flabellate manner ; acute at the 

 base. Length 1-1 440th. On marine Alga?, Trieste. 



P. dehilis (Kiitz.) — NaiTowly cuneate, rather acute at' the base, 

 sub-flabbellate. Length 1-1 380th. On stems of sea Alga). 



P. hyalina (Kiitz.) — Cimeate, rather acute at the base, with closely 

 arranged pores (vittfe) ; laterally, obovate-pyriform ; hyaline (P. 16, 

 f. 13a.) Length l-570th to l-480th. 



Var. fb.) r«f^;«os«.— Obsoletely stiped. North Sea, Heligoland, 

 England. 



P. tenuis (Kiitz.) — Linear, cuneate, slender, acute at the base. 

 Length 1 -480th. Cliristiana, Sweden. 



P. Jurgensii (Kiitz.) — Broadly cuneate, truncate at the base. 

 Length 1 -432nd. On marine Algae, North Sea. 



Genus Ehabdomena, (Kiitz.) — Bacilli tubular, concatenate, stipes 

 lateral, interruptedly vittate, and transversely striated ; vittae capi- 

 tate ; striae transverse, forming numerous longitudinal rows. 



This genus is included in the family Striatellece (Kiitz.) ; one form 

 only has been previously noticed by Ehrenberg, who has described it 

 as a member, both of the genus Tessella, and also of Striatella, i. e., 

 the same form under two names, according to the accidental circum- 

 stance of having met with a solitary, free, or an attached frustule. 

 All the forms of RhaMonema are marine. 



R. minutum = Tessella Catena (Ealfs.) — Small, with a double row 

 of marginal vittae ; transverse stria? very delicate. Length 1-1 200th. 

 On Conferva, English Coast ; Baltic. 

 E.. arcuatum = Tessella catena and Striatella arcuata, (Ehi\) 

 E. Adriatieum. — Large, with four seriesof vittoB, viz., two marginal 

 and two median; striae transverse, distinct. Length 1 -480th to 

 l-168th. (P. IG, f. 27.) In Adriatic and Mediterranean. 



Genus EiiiPTDoriroRA, (Kiitz.)— Bacilli, on primaiy side, cuneate; 

 on the other side, obovatc, lanceolate, stalked. 



