53 



COSCINODISCUS. 



C. nobilis Grun. (J.R.M.S., 1879, P- 687, pi. 21, f. 1*) plate 34, 

 fig. goo. 



Valve very large, with fine puncta arranged in radiating rows, interrupted 

 here and there by hyaline lines, leaving at the centre of the valve a consider- 

 able rounded hyaline space. Diameter of the valve, 37 to 54 c.d.m.; about 

 7 puncta in i c.d.m. 



Marine. Found in Noctilucce and Ascidias at different points on the English Coast, and 

 probably will be found in Belgium. 



This form has often been confounded with C. Concinnus, from which it is 

 distinguished by its smooth central space. 



Group II Alveoli. Valve with distinctly cellular structure. 



C. radiatUS Ehr. (Kreideth, pi. 3, f. 1, a.b.c. ; Ad. Schm. Atl., pi. 

 60, f. 9, etc. ; H.V.H. Atl., pi. 129, f. 5*; Type No. 529), plate 23, fig. 

 663. 



Valves with alveoles arranged in radiating rows, about 2 to 2*5 in 1 c.d.m., 

 of the same size throughout, except near the margin, where there is a zone of 

 smaller alveoles (about 5 to 6 in 1 c.d.m.). Alveoles punctate, distributed 

 throughout the valve, and not leaving a hyaline space at the central portion. 

 Size excessively variable ; mean size of Belgian specimens, 5 to 7 c.d.m. 



Marine. Blankenberghe, and on all the coasts of the North Sea. Forms of all dimensions 

 found. England (Kitton, Stolt., Norman, Comber). Ireland (O'Meara). 



The above description corresponds with the form which Mr. Grunow 

 considers as the type-form, but there are all possible varieties both in size and 

 in the size of the alveoles. 



var. Oculus-Iridis Ehr. (Type No. 528). 



Central alveoles grouped stellately, much larger than the others, and 

 very slightly or not punctate ; medium sized alveoles, about 3 to 4 in 1 

 c.d.m. in the typical variety; alveoles of margin twice as small. 



The largest specimens of this form observed by Mr. Grunow attain as 

 much as 30 c.d.m. 



Marine. Rare. Blankenberghe, 2nd Basin. Scheldt at Antwerp, and on all the coasts 

 of the North Sea. Ireland (O'Meara). 



var. Asteromphalus Ehr. (H.V.H. Atl., pi. 130,!. 1, 2 and 5*; 

 in Type No. 508), plate 23, fig. 664. 



Similar to the last variety, from which it only differs by the strong 

 punctuation of the central alveoles ; this punctuation is sometimes 

 excessively obvious {forma conspicua Grun.). 



Blankenberghe. Very rare. Cuxhaven. England (Stolt). 



