COSCINODISCUS. 531 



var. centralis (Ehr.) Rattr. 



Differs from the preceding by the presence of two asymmetrical 

 apiculi difficult to be seen in balsam. 



Marine. North Sea, numerous localities. England (Norman). Ireland (O'Meara). 



var. concinnus W. Sm. 



Valves with central alveoles grouped stellately, distinctly punctate ; 

 median alveoles very small, forming 7 to 10 radiant rows in r c.d.m. 

 Margin furnished with a circlet of small subm.irginal spines, rather 

 approximate and unequally distant. Diameter of Belgian specimens, 

 about 20 c.d.m. 



Blankenberghe 2nd Basin, rather common, and on all the coasts of the North Sea. 

 England (Kitton, Stolt., Norman, Comber). Ireland (O'Meara). This species is very 

 fragile and is generally only met with in fragments. It i; found in great abundance in a 

 pelagic state both in the Scheldt and in the North Sea (H.V. H.). 



var. Jonesianus H.V.H. (Eupodiscus foncsianus Grev. ; E. ? 

 commutatus Grun. ; Coscinodiscus Grun. in Franz Jos. Ld., p. 79 ; 

 H.V.H. in Type No. 490). 



This is only an appendiculate form of the preceding variety. The 

 marking of the valve and the central rosette differentiates at first view 

 the form from a true Eupodiscus. I have therefore given it the name of 

 subvarietas yoncsiana. It is clearly characterised by the two asymmetrical 

 processes and by the row of dots or small spines which form a complete 

 sub-marginal circle. 



This form is not very rare in the North Sea (H.V.H.). It is some- 

 times met with in a triangular form. I have also a specimen in my 

 possession from Java. The processes are not coincident with the angles, 

 but are placed in the middle of the margins. 



Note. In his work on the diatoms of Franz Josef's Land, Mr. Grunow 

 states that all these forms are connected with one another by all possible 

 variations, and that it is best to unite them under the name of C. radiatus, 

 the first species of the group which has just been described. 



C. excentricus Ehr. (Kutz. Baa, p. 131, pi. 1, f. 9 ; h.v.h. Atl., 



pi, 130, f. 4, 7 and 8* ; Type No. 530), plate 23, fig. 666. 



Valve circular, margin furnished with numerous small spines ; alveoles 

 diminishing gently and gradually up to the margin, where is found a very 

 narrow zone of much smaller alveoles. The rows of alveoles form eccentric 

 lines; about 5 rows in 1 c.d.m. at the centre of the valve. Diameter, 5 to 6 

 c.d.m. 



Marine. Very frequent; Blankenberghe, Antwerp, England (Kitton, Stolt., Norman, 

 Comber). 



