THE DIATOMACE.E OF PHILADELPHIA AND VICINITY 27 



ACTINOCYCLUS BARKLEYI VAR. AGGREGATA RATTR. 



Surface flat from centre to semi-radius. Central space irregular, sometimes with a few 

 scattered granules. Markings round with central dots distinct, about 7 at the centre, de- 

 creasing in straight radial rows to 12 in 10 n at the border, where they form moniliform striae. 

 Border narrow with striae about 16 in 10 ju. Hyaline interspaces at the origin of the shorter 

 rows, but not at equal intervals. At the border, linear hyaline spaces occur at somewhat 

 irregular intervals between the moniliform striae owing to the termination of certain radial 

 rows before they reach the circumference. Nodule small, from one-seventh to one-fourth 

 the radius from the border. 



According to Rattray the distinction between A. ralfsii and A. barkleyi is partly in the 

 absence of the zone arrangement of the hyaline spaces in the latter, and to the slight dif- 

 ferences in the number of granules. The variety aggregata differs from the type form of 

 barkleyi mainly in the distance of the nodule from the border. I have specimens from the 

 blue clay material at Walnut St. Bridge, and from Smith's Island, in which the distance 

 from the border in one case is, as stated above, quite different from that in the other. In 

 specimens from Morris Cove, Conn., the locality referred to by Rattray, variations occur. 



Blue clay. 



PL 6, Fig. 1. 



In the figure the subulate hyaline spaces at the border are, in some instances, wider 

 than usual. 



ACTINOCYCLUS MONILIFORMIS RALFS 



Surface flat, from centre to about five-sixths of the radius. Central space rounded, 

 with one or more granules. Markings, 8 in 10 n, round, in radial rows, fasciculate, the oblique 

 transverse rows irregular, very slightly decreasing until near the edge of the flattened zone, 

 and then suddenly decreasing and appearing as decussating lines oblique to the border. 

 Apiculi distinct, interfasciculate within the border. Nodule quite evident, surrounded by 

 a rather wide irregular hyaline space on the margin of the flattened zone in the middle of 

 the fasciculus. Border wide, with striae about 20 in 10 /*. 



Blue clay. Port Penn. Not common. 



PI. 6, Fig. 2. 



Equivalent to Actinocyclus ehrenbergii, H. L. S. Type Slide 10. 



In a valve from Port Penn, Delaware Bay, two nodules occur nearly opposite each 

 other. 



ACTINOCYCLUS ELLIPTICUS VAR. DELAWARENSIS N. VAR. 



Valve rhombic-elliptical. Markings somewhat angular, 6 in 10 ju at the centre where 

 they are sub-concentric, thence decreasing in lines radiating more or less toward the bor- 

 der, where they suddenly become punctiform, striae about 20 in 10 n. Border equal to one- 

 fifth the radius. A nodule is found on the inner side of the border. Apiculi apparently 

 absent. 



The markings are larger than in the Richmond forms which are associated by Rattray 

 with Actinocyclus ellipticus Grun. The form corresponds closely to Witt's Cestodiscus 

 ovalis var.? (Witt, Polirschief. von Archangelsk-Kurojedowo, PI. 8, Fig. 2), except as to 

 the border. It does not answer to Van Heurck's figure or any other. 



Blue clay. Very rare. 



PI. 3, Fig. 6. 



