APPENDIX. 435 



782. NAVICULA folium. Shell-like lorica ovate, turgid 

 and obtuse, slightly compressed, central aperture not pre- 

 sent, striae narrow, twenty-four being in the l-96th of a 

 line. Length 1 -540th. 



783. NAVICULA gemma. Shell-like lorica ovato-oblong, 

 large, turgid; central aperture not present; striae slender, 

 sixteen being in the l-96th of a line. Found alive at the 

 mouth of the Elbe. Length l-290th to 1 -220th. 



784. NAVICULA Norwegia. Shell-like lorica, viewed 

 laterally, linear, narrow and truncated at both ends ; from 

 the back, broadly ovate, and acute at the extremities; cir- 

 cumference with a narrowly striated margin, area smooth. 

 The l-96th of a line contains thirty striae. The N. prae- 

 texta of the Greek chalk marl is very similar to this 

 species. Found alive, in sea water, at Christiana. Length 

 l-360th. 



785. NAVICULA quadrifasciata. Shell-like lorica, viewed 

 laterally, narrow, linear, and truncated from the back, broad 

 and acute at both ends; margin broad. "The central fur- 

 rows of the mouth and dorsal surface divides the central 

 striated longitudinal bands into two portions, from which, 

 along with the two lateral bands, four striated bands ap- 

 pear, the two central ones being interrupted by the mouth/ 5 

 In the l-96th of a line there are twenty striae. Found 

 fossil in the chalk marl of Greece, and alive in sea water 

 at Christiana; ova greenish, or rusty yellow, in the live 

 creatures. Length 1-4 30th. 



786. PEBIDINIUM pyrophorum. Found fossil in chalk 

 flints at Gravesend. Length 1 -560th. 



On the Locomotive Organs in some Naviculae. 

 In the small pools left by the ebb of the tide near Cuxhaven, 

 Dr. Ehrenberg remarked numerous little bodies, apparently 

 similar to Navicula, Surinella elegans, and S. striatula, 

 but which, from their comparatively very great size and 

 structure of lorica, were easily distinguishable from the 



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