DIATOMACE^E. 



[ 256 ] 



DIATOMACE^E. 



afterwards forming a zigzag chain ; 

 vittee two, longitudinal, interrupted at 

 ends, and more or less figured ; marine 

 (PL 1. figs. 14,15). 



Diatomella. Fr. quadrangular ; vittae 

 two, interrupted in the middle and at 

 each end (PI. 61. fig. 16). 



Tribe III. Areolatce. Valves circular, with 

 cell-like (areolar) markings, visible by ordi- 

 nary illumination. 



Subtribe 1. Disciformes. Valves alike, with- 

 out appendages or processes. 



Coh. 14. COSCINODISCEJE. Valves circular. 



Actinocyclus. Fr. solitary; v. circular, 

 undulate, the raised portions appearing 

 as rays or bands radiating from the 

 centre, which is free from markings; 

 marine and fossil (PL 25. fig. 17). 



Actinoptychus. Fr. as in Actinocyclus, 

 but radiating internal septa, as well as 

 rays ; marine and fossil (PI. 25. fig. 16). 



Coscinodiscus. Fr. single; v. circular, 

 areolar all over; marine and fossil 

 (PL 61. fig. 1 ; PL 25. figs. 7, 8). 



Arachnoidiscus. Fr. single ; v. circular, 

 not undulate, with concentric and 

 radiating lines, and intermediate are- 

 olae, absent from the centre (pseudo- 

 nodule); marine and fossil (PL 16. 

 fig. 12). 



Asterolampra. Fr. single; v. circular, 

 finely areolar, except in the centre 

 and on equidistant clear marginal ra^s 

 radiating from the centre, which is 

 traversed by radiating dark lines 

 (septa) alternating with the marginal 

 rays; fossil (PL 25. fig. 5). 



Aster omphalos. As Asterolampra, but 

 two of the central dark lines parallel, 

 and the corresponding marginal ray 

 obliterated ; fossil (PL 25. fig. 2 ; PL 

 18. fig. 15). 



Halionyx. Fr. single ; v. circular, with- 

 out septa, with rays not reaching the 

 centre, and with intermediate shorter 

 rays; between the rays transverse 

 (concentric?) areolar lines; fossil (PL 

 18. fig. 51). 



Odontodiscus. Fr. single, lenticular; v. 

 covered with puncta (areolse) arranged 

 in radiating rows or excentrically 

 curved lines, and with erect marginal 

 teeth; fossil (PL 18. fig. 52). 



Omphalopelta. As Actinoptychus, but 

 upper part of margin of valves with a 



few erect spines; fossil (PL 18. fig. 

 63). 



Symbolophora. Fr. single, disk-shaped; 

 v. with incomplete septa radiating 

 from the solid angular umbilicus, and 

 intermediate bundles of radiating lines ; 

 marine and fossil (PL 25. fig. 6 ; PL 18. 

 figs. 64, 55, 56). 



Systephania. Fr. single; valves circular, 

 areolar, -without rays or septa, with a 

 crown of spines or an erect membrane 

 on the outer surface of each valve; 

 fossil (PI. 18. figs. 57, 58). 

 Coh. 15. ANGULIFEILS:. Valves angular. 



Amphitetras. Fr. at first united, after- 

 w 7 ards separating into a zigzag chain, 

 rectangular; v. rectangular, the an- 

 gles often produced; marine (PL 16. 

 %?). 



Amphipentas. Fr. solitary ; v. penta- 

 gonal ; fossil (PL 25. fig. 11). 



Lithodesmium. Fr. united into a straight 

 filament ; v. triangular, one side plane, 

 the others undulate; marine (PL 17. 

 fig. 4). 



Tribe IV. Appendiculatce. Valves with 

 processes or appendages, or with the angles 

 produced or inflated. 



Coh. 16. EFPODISCE^:. Fr. disk-shaped ; 

 v. circular. 



Eupodiscus. Fr. single, disk-shaped ; 

 v. circular, with tubular or horn-like 

 processes on the surface; freshwater 

 and marine (PL 16. figs. 30, 31). 

 [Auliscus. As Eupodiscus, but processes 

 obtuse and more solid ; fossil (PL 18. 

 fig. 60). 



Insilella. Fr. single, fusiform ; v. equal, 

 with a median turgid ring between 

 them = terete Biddulphia; marine.] 

 Coh. 17. BIDDULPHIEJE. Fr. flattened ; v. 

 elliptical or suborbicular. 



Siddulphia. Fr. rectangular, more or 

 less united into a continuous or zigzag 

 filament ; the angles inflated or pro- 

 duced into horns; v. convex, centre 

 usually spinous ; marine (PL 16. fig. 

 15; PI. 19. fig. 9). 



Isthmia. Fr. rhomboidal or trapezoidal, 

 cohering by one angle; angles pro- 

 duced; marine (PL 17. fig. 2). 



Chcetoceros. Fr. compressed ; v. equal, 

 with a long spine or filament on each 

 side ; marine (PL 50. fig. 47). 



Rhizoselenia. Fr. elongate, subcylindri- 

 cal, marked with transverse or spiral 



