HYDROSERA. 



453 



My genus Terpsino'e comprehends the genus Pleurodesmium Kutz, 1S46, 

 which is only differentiated by the frustules being united by the intermediary of 

 short processes in the form of feet, and also the genus Telragramma Ekr., 

 1843, which has as its unique characteristic, the possession of valves with fine 

 costae. 



*<&*. e. <TtT I ....*.*w..v.*;.. v.\. 1 a j "tj 



&Z4* - !%?& 



a. b. 



Fig- *77 T. {Pieurodesmium) Brcbissonii. 

 a. Valve view. b. Girdle view. 



We figure in the text T. musica 

 (fig. 176), the typical form of the 

 genus and T. {Pleurodesmium) 

 Brcbissonii {Kutz.) (fig. 177), 

 These forms belong essentially to 

 the torrid regions. On one occasion 

 I found a specimen of T. {Pleuro- 

 desmium) Brebissonii in the mud 

 of the -Scheldt at Antwerp, but it 

 had evidently, in my opinion, 

 been brought there by a ship 

 coming from tropical regions. 



GENUS 118. HYDROSERA WALL., 1858. 



Valve triangular or com- 

 pressed, with cellular struc- 

 ture, constricted at the apices 

 which are broadly rounded. 

 Girdle face quadrangular, 

 areolate, with connecting 

 membrane finely punctate. 

 Frustults united in bands. 



Fig. 178. Hydrosera triquetra. 



Grunow and H. L. Smith unite the genus Hydrosera with Pleurodesmium 

 and Terpsi/we, which have the same structure. It appears to me that the 

 angular asymmetrical form enables this genus to be distinguished from the 

 preceding as is done by Deby and De Toni. 



