THE DIATOMACE^E OF PHILADELPHIA AND VICINITY 23 



COSCINODISCUS RADIATTJS EHR. 



Markings polygonal, slightly decreasing toward the border where they are much 

 smaller; border well marked, striate. Quite variable in size. 

 Common in the blue clay and along the coast. 

 PI. 3, Fig. 11. Fig. 1 is probably a smaller form. 



COSCINODISCUS SUBATJLACODISCOIDALIS RATTR. 



Markings small, decreasing toward the border in somewhat fasciculate rows. About 

 one-third the distance from the border are five (Rattray finds six) well-marked apiculi 

 somewhat resembling those of Aulacodiscus. Border narrow, hyaline. 



Rare in the lower stratum of the blue clay. 



PL 3, Fig. 4. 



COSCINODISCUS ARGUS EHR. 



Markings angular with central dots, increasing from the centre toward the border, 

 where they are smaller. 

 Blue clay. 

 PL 3, Fig. 7 (a small form). 



COSCINODISCUS BIANGULATUS SCHMIDT 



Central space and rosette absent, markings large, angular, not punctate, with large 

 central papillae, decreasing toward the border. Border wide, coarsely marked with rows of 

 granules, and with two indentations on the inner side distant from each other about two- 

 thirds of the diameter. 



Blue clay. 



PL 3, Fig. 3. 



Distinguished from Coscinodiscus asteromphalus var. omphalantha Grun., which 

 also has two constrictions, by the absence of punctate markings. 



COSCINODISCUS ASTEROMPHALUS EHR. 



Central space small, surrounded by a rosette of large polygonal cells from which radiate 

 hexagonal cells, increasing about half way toward the border and then slightly decreasing. 

 Cells punctate. 



Blue clay. 



PL 2, Fig. 16; PL 40, Fig. 12. 



COSCINODISCUS ASTEROMPHALUS VAR. OMPHALANTHA (EHR.) GRUN. 



Central space absent, rosette evident. Markings 2^ in 10 jit, somewhat smaller near 

 the rosette and decreasing near the border, which is constricted in two places, as in C. 

 biangulatus. 



Blue clay. 



PL 38, Fig. 10. 



COSCINODISCUS OCULUS-IRIDIS EHR. 



Central space and rosette distinct; markings polygonal, not punctate, with large 

 papillae, smaller near the rosette, increasing toward the semi-radius, and then decreasing to 

 the striated border which is comparatively narrow. 



Blue clay and Atlantic coast. 



PL 3, Fig. 10. 



