THE DIATOMACELE OF PHILADELPHIA AND VICINITY 29 



AULISCUS SCULPTUS (WM. SM.) RALFS 



Valve elliptical or subcircular, median areas distinct, rounded, circumscribed by coarse 

 distant costse radiating near the border where they are more evident, and converging to- 

 ward the processes. Central space rounded, sometimes indefinite. Processes, two, circular. 



Typical specimens show wide, coarse, distant costse, but, in some cases, the median 

 areas are indistinctly outlined. 



Blue clay. 



PI. 5, Fig. 5. 



AULISCUS CvELATUS BAIL. 



Valve elliptical or subcircular, with radiating costse, more evident around the median 

 areas and at the border, converging toward the processes, with intermediate punctate 

 radiating lines. Central space rounded or irregular. Processes circular. 



A. sculptus has coarser costse and the interspaces are hyaline, or apparently so, while 

 in A. cselatus the punctate strise between the costse are more evident. 



Blue clay. Not uncommon. 



PL 5, Fig. 4. 



Fig. 7 is a small, indefinite form intermediate between A. sculptus and A. cselatus. 

 The numerous variations in this genus make it difficult to satisfactorily differentiate the 

 species. The size of the four above described varies from 40 to 150 n- 



PSEUD AULISCUS A. S. (1875) AND LEUDUGER-FORTMOREL (1879) 

 Valve circular or subcircular, nearly flat or depressed at the centre. Central space not 

 evident. Processes circular, with narrow border, near the circumference. Border narrow, 

 striated. Markings granular, radiating, sometimes interspersed with strise and apiculi. 

 Differs from Auliscus chiefly in the absence of a central space and costse. 



PSEUDAULISCUS RADIATUS (BAIL.) RATTR. 



Valve circular, or nearly so, flat. Central area with scattered granules radiating and 

 increasing in size outward in diverging rows toward the border which is coarsely striated. 

 Processes, two, circular. Two small apiculi are inserted at about one-fifth the radius from 

 the border near the ends of the minor axis. 



Blue clay. Rare. 



PL 5, Fig. 9. 



The apiculi are not always figured. They appear in a number of specimens from the 

 Miocene of Maryland, Atlantic City, Harvey Cedars and Newbern. 



PSEUDAULISCUS SPINOSUS (CHRISTIAN) RATTR. 



Valve subcircular or slightly quadrangular, depressed at the centre and rising to an 

 elevated zone near the border, the two zones separated by a distinct line. The inner zone 

 indistinctly reticulate with fine puncta radiating from the centre and apiculi at intervals. 

 The outer zone with smaller apiculi surrounding the inner zone and with intermingled rows 

 of fine puncta and interrupted diverging strise. Near each end of the minor axis is a rather 

 long, robust spine inserted at one-fourth the radius from the border which is narrow and 

 striated. Processes circular, close to the circumference. 



Auliscus spinosus Christian. 



Blue clay. Rare. 



PL 5, Fig. 10. 



The genus is named by Schmidt, described by Leuduger-Fortmorel and emendated by 

 Rattray. 



