THE DIATOMACEJ3 OF PHILADELPHIA AND VICINITY 25 



ACTINOPTYCHUS HELIOPELTA GRTJN. VAR.? 



Valve circular, sectors, eight, umbilicus circular, without rays ; border wide, cellular, 

 with distinct rays. Inserted at a distance within the inner edge of the border are large 

 processes, one on each of four alternate sectors, and two on each of the others. The sectors 

 are cellulate and punctate. 



Near A. heliopelta var. versicolor Brun., which, however, in the specimen in my collec- 

 tion from Atlantic City (artesian well), has a greater number of processes and they are 

 situated on the edge of the border. 



Outcrop at Buckshutem, N. J. Rare. 



PI. 4, Fig. 3. 



It has been quite well determined, I think, that the typical forms of A. heliopelta 

 occur at the base of the Miocene. At Rock Hall, Md., on the eastern shore of Chesapeake 

 Bay, at a depth of from 21 to 130 ft., and at Wildwood, N. J., at a depth of from 78 to 179 

 ft., diatomaceous beds occur considered by Mr. Lewis Woolman (Geol. Surv. of N. J., 

 1898, pp. 116-121) "as synchronous in age," the former being deposited in the Delaware 

 River Delta and the latter in the Chesapeake in post-miocene times. In each of these beds 

 a small form of A. heliopelta is rarely found. The material at Buckshutem is post-miocene, 

 and the form here figured shows a marked variation from the Miocene species and a 

 gradual approach toward A. undulatus. 



POLYMYXUS L. W. BAIL. (1855) 



Valve circular, usually divided into fourteen sectors which are on the same plane at the 

 centre, but the alternate ones are elevated into mammillated projections terminated by 

 small processes on the margin. Zone view rectangular with undulations subconical, 

 terminated by the processes. 



POLYMYXUS CORONALIS L. W. BAIL. 



Central space hyaline, rounded or slightly stellate, from which radiate rows of fine 

 puncta in quincunx, shown in the figure only on the alternate elevations, the depressed 

 interspaces being out of focus. The mammillae are stated by Bailey to vary from six to ten. 

 Very rare in the blue clay (Walnut St. Bridge). Occurs also in the Wildwood deposit 

 (Bull. Torrey Bot. Club, 1895, p. 261). 

 PL 4, Fig. 7, and PL 5, Fig. 2. 



A^/A cef 



3. EUPODISCEJE< 



~~"*Aulacodiscinoe. Valves with mammiform elevations near the border surmounted by 

 nipple-like processes. 



AULACODISCUS THE ONLY GENUS AS ABOVE 



Eupodistinoe. Valves with ocelli. 



(1) Actinocyclus. Valve with one small ocellus; striae radial. 



(2) Eupodiscus. Valve with one or more ocelli; striae not radial. 



(3) Auliscus. Valve with large, elevated ocelli. Central area hyaline. Markings 

 granular and costate. 



(4) Pseudauliscus. Valve with radiating granules. No central space. 



