CORETHRON. 423 



simple and more or less curved in the terminal individuals. Frustules united 

 by about 20 in a filament. 



Marine. Rare. Blankenberghe, 2nd Basin; ; floating in the Scheldt. (H.V.H.). Stomachs of 

 Noctiluca, Yarmouth (Kitton).' Surface of Dee, England. Common (Stolt. ). East Coast of 

 England (Norman). 



Note. The forms for which Ehrenberg constituted the genus Actiniscus 

 were not diatoms, and subsequent authors who have written on these forms 

 have not admitted them in their classification. Ehrenberg included the genus 

 Bacteriastrum in his genus Actiniscus, but without any plausible reason, and 

 he continued to do so until his last work, Fortsetzung dcr Mikr. Studien, 1S75. 

 All the forms of Bacteriastrum ought to be included in the g^nus Chcctoccros 

 (Note by Mr. Kitton). 



Sub-genus III. Corethron Castr., 1886. 



Valves convex, furnished 

 with a corona of erect spines. 

 Frustules cylindrical. 



As will be noticed, the differ- 

 ence between Bacteriastrum and 

 Corethron' consists in the spines 

 of the first genus being placed 

 horizontally, while in Corethron 

 Fig. 140. Corethron hispidum Castr. they are erect. Hitherto five 



species have been described, none of which inhabit our shores. 



