THE DIATOMACE.E OF PHILADELPHIA AND VICINITY 17 



Conferva nummuloides Eng. Bot. pi., 2287, not Dillwyn. 

 Meloseira barren Grev. 



Lysigonium nummuloides (Lyngb., Kuetz.) O'Meara=Gaillonella nummuloides (Dillw.) 

 Bory. See O'Meara, p. 248. 



Marine and brackish. Long Island Sound and coast of New Jersey. 

 PL 1, Fig. 7. 



LYSIGONIUM VARIANS (AG.) DE TONI 



Frustules cylindrical, in long filaments, slightly constricted on each side of the suture; 

 puncta in oblique rows in zone view. Valves 15-35 M in diam. (De Toni), sub-plane, with 

 fine puncta in lines radiating from the centre. Under medium magnification the frustules 

 appear smooth. Very variable in size. 



Meloseira varians Ag. 



Fresh water. Common in ditches and springs. 



PL 1, Figs. 18 and 19. 



HYALODISCUS EHR. (1845) 

 (hyalos, transparent, and discus, a disc) 



Frustules spheroidal; valve with a flattened, irregularly punctate umbilicus from which 

 proceed radiating or decussating lines of fine puncta. 



ANALYSIS OF SPECIES 



Valves divided into sectors stelliger 



Valves not divided but interrupted by short dark lines at intervals .... radiatus 



Valves with very fine puncta scoticus 



HYALODISCUS STELLIGER BAIL. 



Valve with puncta in oblique decussating rows which, by reason of the difference in 

 obliquity, form numerous sectors. Umbilicus irregular, with scattered, coarse puncta. 

 Margin wide, striated. 



Podosira maculata Wm. Sm. 



Blue clay. Not common. 



PL 1, Fig. 22. 



HYALODISCUS RADIATUS VAR. ARCTICA GRUN. 



Valve with radiating puncta from a rather small umbilicus, the rays interspersed with 

 short, dark lines, having the appearance of spines, at irregular intervals. Margin broad, 

 striated. 



Pyxidicula radiata O'Meara. 



The Philadelphia form corresponds exactly to Grunow's variety which has closer 

 puncta than the type form. 



Blue clay. Rather rare. 



PL 1, Fig. 21. 



