286 COCCONEIS. 



GENUS 34. COCCONEIS (EHR. 1835), GRUN, 1868. 



Valves broadly oval, elliptic or discoid, rarely lanceolate ; the upper 

 having only a pseudo-raphe, the lower furnished with nodules and a 



a. b. c 



Fig. 65.- Cocconeis Scutellum. 

 a. Upper valve, b. Lower valve, c. Annulus. 



true raphe. Frustules arched or genuflexed, living as a parasite on 

 other algae. Endochrome as in the Achnanthes. 



The genus Cocconeis includes numerous and varied species. It has been 

 skilfully divided by Prof. Cleve into a certain number of groups which may 

 be considered as subgenera or even as genera if that be preferred. The 

 following are the groups which I adopt to distinguish my species : 



ANALYSIS OF GROUPS. 



Valve f Upper valve furnished with distinct costae 



having a -1 



marginal (, Upper valve punctate, striate . 

 ring. 



f 



| Valve elliptic 



Valve 



having 



neither 



interior 



skeleton 



nor ring. 



f Upper 



valve 



furnished 



with 



costae. 



Upper 



valve 



without 



costae. 



| Valve lanceolate 



I 



Upper valve with a broad axial area 



f Valve elliptic or broad 



1. Pleuroneis. 



2. Cocconeis. 



3. Disconeis. 



4. Actinoneis. 



5. Heteroneis. 



6. Eucocconeis. 



-\ Upper valve 



with narrow -J 



axial area. j Valve linear or lanceolate, 



t I with fine puncta . 7. Microneis. 



* Valve having a separate marginal ring. 



Group i. Pleuroneis Cleve. Upper valve furnished with distinct 



costae. 



P. COStata (Greg.) Cleve; (C. Costata Greg., Q.J.M.S. 1855, iii., p. 39, 

 pi. 3, f. 10 ; H.V.H. Atl., pi. 30, f. 11-12*3 Pleuroneis Costata Cleve in litt.), 

 plate 29, fig. 816. 



