414 DESCElPTiON OF [Poli/ffastrica- 



dotted lines ; tlie puncta aiTanged in a quincunx. Has the habit at 

 of N. amphishana. 



NayicTjLA lej^tosfi/Ius. This fossil species, and the seven following, 

 were discovered by Ehrenberg in earth from Ireland. 



N. Cocconeis. 



N. AmpMrrina. 



N. osmlata. 



N. hirostrts. Probably Stauroneis hirostris. 



IS. Sti/lus. 



IS. amphiata. 



N. mesopachya. 



N. diaphana. — Large, elongate, lanceolate ; apices obtuse ; surface 

 very smooth, diaphanous ; umbilicus not perforating ; a double lon- 

 gitudinal line down the centre. Habit of Stauroneis Phcenicenteron. 

 (l-192nd.) 



N. I)emerar<2. — Smaller ; oblong and smooth ; venti-ally, rhomboid, 

 and tumid; apices acute, attenuate, and subrostrate. Length 1-576'Lh. 



!N. Schomburglcorum. — Large, elongate, lanceolate, with obtuse ex- 

 tremities, and the habit of N. diaphana, but with three longitudinal 

 lines (sulci) on each side the umbilicus. Length 1-1 80th. Alive in 

 Guiana. 



Nageli describes (Report Ray Society, 1846, p. 221,) what he 

 assumes to be a new species of Navicula, nearly allied to JVavictda 

 striata (Ehr.) = Surirella Striatula (?). He found it in brooks 

 about Zui'ich ; it exhibits no movement. The contained matter is 

 brown, and fills the whole of the central cavity, except the horns 

 (prolonged extremities), which are ti^ansparcnt and uncoloured. 



Nageli adduces this species as illustrating the existence of a 

 nucleus and nucleolus in the interior ; and it is in it also that he 

 " observed a pretty rapid circulation of the granular contents, the 

 gi'anules passing from the nucleus outwards, along the edges, and 

 back again to the former." 



Kiitzing divides his genus Kavictda into six sections ; it includes 

 numerous species of the genus Pinnulm'ia, as that natui-alist does not 

 recognize the presence or absence of transverse striae as a generic 

 distinction. In his recent volume, " Species Algarum," he enume- 

 rates 179 species, including nine doubtful; most of them are de- 



