22 THE DIATOMAC&E OF PHILADELPHIA AND VICINITY 



toward the border, the rows parallel to the central row of each fasciculus. Border narrow 

 with fine striae; apiculi often present between the fasciculi. 



Blue clay and along the coast. Very common in the water supply of Philadelphia and 

 Camden, where the diameter seldom exceeds 40 M and the markings on the semi-radius are 

 10 in 10 M- 



PI. 2, Fig. 17. 



COSCINODISCUS DENARIUS SCHMIDT 



Markings larger than in C. subtilis, equal, forming usually ten fasciculi, each begin- 

 ning near the semi-radius and containing ten parallel rows of granules. 

 Common in the blue clay and sparingly along the coast. 

 PL 2, Fig. 13. 

 Forms are found intermediate between C. subtilis and C. denarius, as shown in Fig. 15. 



COSCINODISCUS POLYACANTHUS GRUN. 



Markings angular, 10 in 10 n, decreasing toward the border, fasciculate. Apiculi large, 

 twelve or more, usually inserted at the middle of each fasciculus, and extending into the 

 interior of the cell. The apiculi in outline resemble the heads of horse-shoe nails, and are 

 seen with difficulty except when the valve is examined from the inner side. Border narrow, 

 striated. Diam. 70 M- 



Pensauken, N. J., artesian well. 



PL 38, Fig. 5. 



Rattray's description of C. polyacanthus var. intermedia Grun., from Cape Wankarema, 

 Siberia, gives the diam. as 60 /*, and there are about 7 markings by actual count in 10 n in 

 Grunow's figure (Diat. Fr. Jos. Land, PL 3 (C), Fig. 25). The apiculi are more numerous, 

 but there appears to be little doubt of the general similarity. The Philadelphia form is 

 abundant in the Pensauken well deposit at a depth of 33 ft. The apiculi become quite dis- 

 tinct in slides stained with silver nitrate by Mr. F. J. Keeley; they are distinct from small 

 apiculi sometimes evident between the fasciculi. The specimens in the Pensauken deposit 

 are mingled with other forms which cannot be distinguished from C. subtilis. Whether the 

 two are identical, I am unable to determine. Rattray (Rev. Cos., p. 47) refers to H. L. 

 Smith's Type Slide No. 100, from rice-field mud, Savannah, Ga., as C. subtilis. In Smith's 

 slide, in my possession, a number of the forms show faint outlines of the large apiculi and 

 are otherwise exactly like C. polyacanthus. 



RADIATI 

 COSCINODISCUS VELATUS EHR. 



Markings angular, decreasing slightly toward the coarsely striated border, covered 

 with fine puncta. 

 Blue clay. 

 PL 3, Fig. 2. 



COSCINODISCUS MARGINATUS EHR. 



Markings rounded, large, decreasing toward the broad border, which is coarsely marked 

 with distant striae. The cells are punctate. 



Common in the blue clay. 



PL 3, Fig. 9. 



In the fossil forms the puncta are not evident, hence the species is usually described as 

 not punctate. 



