566 



IV. COSCINODISCUS Ehbg., 1838. 



8. C. radiatus Ehbg., incl. C. ocalus iridis Ehbg. and C. asterom- 



phalus Ehbg. 



Common around the Færoes, and found all the year round; it reaches 

 its maximum in the winter from December to April and constitutes then 

 the dominant species of the poor >I)isco-plankton<. [See tables.] 



As there is no distinct limit between the 



small specimens (the typical C. radiatus) and 



the larger ones which have been named 



C. ocalus iridis and C. asteromphalus, I prefer 



to take them as one species. It is a marine 



ubiquist which is indifferent as regards sali- 



nity and temperature. 



9. C. concinnus W. Smith, Syn. Brit. Diat., 



II., p. 85. 



Rather common and found during most of 

 the months: it reaches its maximum in February 

 —April and is then common. A temperate, neritic 



species which has its central area of distribution in the North Sea. 



[See tables.] 



10. C. subtilis Ehbg. 



Rare; only found in a few samples during the winter months. Not 

 a true plankton-form. 



11. C. lineatus Ehbg. 



Rare; found in three samples. Not a true plankton-form. 



12. C. excentricus Ehbg. 



Rare; in some of the samples forms occur which are not distin- 

 guishable from Thalassiosira gelatinosa, and perhaps this species has 

 sometimes been mistaken for the species in question and vice versa. 



Fig. 122. Coscinodiscus concinnus 



W. Smith. A cell with several 



connecting rings and much 



arched valves ( 2ll "/i). 



ACTINODISCEAE. 

 V. ACTINOPTYCHUS Ehbg., 1839. 

 13. Actinoptychus undulatus Ehbg. 



Not rare in the samples all the year round, but usually in a few 

 specimens only; most frequent in winter. Not a true plankton -form, 

 but a temperate, littoral form. [See tables.] 



VI. ASTEROMPHALUS Ehbg., 1844. 

 14. A. heptactis (Bréb.) Ralfs. in Pritch. In!, p. 838, PI. VIII, lig. 21. 

 Occurs rarely and singly in the samples; it is a true plankton-form, 

 which belongs to the temperate North Atlantic Ocean. 



