CENTROP0RUS. 



449 



{ 



ANALYSIS OF SPECIES. 

 Valve apparently divided into compartments, striation very distinct . H. stelliger. 



Valve not divided into compartments, striation extremely delicate . H. subtilis. 



H. subtilis Bail. (New spec, 1854, p. 10, f. 12; CI. and Moll. 

 Diat., No. 2, sub. H. Franklini E.) 



Valve orbicular, convex, not apparently divided into compartments ; 

 umbilicus, very distinct, coarsely punctate, with irregular, jagged margins. 

 Valve apart from the umbilicus, apparently hyaline, with very delicate 

 structure, puncta in lines crossing one another, forming 24 to 26 striae in 

 1 c.d.m. at the median part of the valve, and attaining as much as 30 at the 

 extreme marginal portion. Diameter, 2 to 10 c.d.m. 



Marine. Authors have not recorded the large form from our regions, but I have found rare 

 specimens, possibly reaching there accidentally, not only on the Belgian coast (Blankenberghe), 

 but also in the mud of the Scheldt. The smaller form inhabits our country, and has been 

 recorded from Scotland, North Wales (Stolterfoth), and has been described under the name of 

 H. scoticus [Kiitz] Grun. ! (= Cyclotella Scotica Kivtz. in Coll. H.V.H. ; H.V.H. Atl., pi. 84, 

 f. 15-18*), plate 35, fig. 917 ( : 600). 



H. Stelliger Bail. (New Spec, 1854, p. 10; Podosira maculata 

 IV. S/n. ; H.V.H. Atl , pi. 84, f. 1,2*; Type No. 454), plate 22, fig. 650. 



Valve orbicular, apparently divided into a large number of compartments. 

 Umbilicus very distinct, finely granular, with irregular margins often laciniate, 

 prolonged so as to form the margins of the compartments. Valve with 

 granules arranged in quincunx, forming about 16 lines in 1 c.d.m. Diameter, 

 3-5 to 8-5 c.d.m. 



Marine. Frequent : Blankenberghe, Ostend, Heyst, Antwerp (Scheldt). England : Norfolk, 

 (Kitton); Surface of Dee, (Stolt.) ; Hull (H.V.H., Type No. 529). Bahnsea. Probably found 

 on all the coasts of the North Sea. 



GENUS 115 CENTROPORUS PANT., 1889. 



Valves convex, orbicular, with broad 

 margin decorated with small arcuate 

 compartments, striolate and separated 

 from the disc by a hyaline annulus. 

 Disc punctate, with fine puncta arranged 

 in radiant rows, centre rounded, with- 

 out puncta. 



This genus only comprises a single 

 form, C. crassus Pant., which we repro- 

 duce here (fig. 174), and which has been 



Fig. 174. Centroporus crass its. 



found in a fossil state at Ananino in Russia. 



v F 



