23* 



RHOICONEIS. 



Fig. 36. 



Rhoiconeis 

 Garckeana Grun. 



we are dealing with a true genus, but only with a craticular state of a 

 Naviculoid form; however, the species of Mr. Weissflog may belong to 

 another genus. 



GENUS 8. RHOICONEIS GRUN., 1863. 



Valves flexed, each furnished with a coarse central 

 nodule. Frustules flexed with connecting zone very 

 developed, showing striae arranged in longitudinal 

 rows. 



This interesting genus resembles on first view an 

 Achnanthes, but it differs from it in that each of the two 

 valves is furnished with a nodule. It includes a dozen 

 species, none of which live on our shores. The figure above 

 represents Rh. Garckeana Grun., photographed from an 

 original specimen of Mr. Grunow. 



GENUS 9. CYMATONEIS CLEVE, 1894. 



(In Synopsis of the Naviculoid Diatoms*). 



Valve divided by longitudinal ridges into 

 two or more divisions. Terminal nodules 

 distant from the apices of the valve. Puncta 

 arranged in longitudinal and transverse rows. 



This beautiful genus is founded on three forms, 

 which are recognized at first sight, but are all unknown 

 to our shores. C. sulcata (Grev.) (JNav. triundulata 

 Gtun.), lives in the Mediterranean and Tropical Seas. 

 C. quadrisulcata {Grun) {Nav. quadrisulcata Grun.) 

 has been found in St. Paul's Island, and C. circum- 

 vallata Cleve is found in the Balearic Islands, Ceylon, 

 Japan, and Labuan. 



GENUS 10.-COLLETONEMA (BREB, 1849) H. VAN 



HEURCK. 



Valve, with structure slightly eccentric ; 

 terminal nodules considerably distant from the 

 apices of the valves from which they are 

 separated by very radiate striae. Frustules 

 enclosed in tubes. Genus forming the con- 

 necting link between Encyonema and Navicula. 



Fig. 37-. 



Cymatoneis 



circumvallata. 



F 'g- 2,%-Colleto- 

 netna lacustre. 



Only one species. 



