DLlTOMACiLE. 



[ 256 ] 



DL^TOMACE^. 



afterwards fonning a zigzag chain ; 

 vittse two, lougitudinal, interrupted at 

 ends, and more or less figured ; marine 

 (PL 1. figs. 14, 15). 

 Diatomella. Fr. quadrangular ; vittse 

 two, interrupted in the middle and at 

 each end (PI. 51. fig. 16). 



Tribe III. AreoJatce. Valves circular, with 

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

 nary illumination. 



Subtribe 1. Disciformes. Valves ahke, with- 

 out appendages or processes. 



Coh. 14. CosciNODiscE^. Valves circular, 



Actinocyclus. Fr. solitary; v. cncular, 

 undulate, the raised portions appearing 

 as raj's or bands radiating from the 

 centre, which is free from markings; 

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



Actinoptychus. Fr. as in Actinocyclus, 

 but radiating internal septa, as well as 

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



Coscinoclisciis. Fr. single ; v. circular, 

 areolar all over ; marine and fossil 

 (PI. 51. fig. 1 ; PI. 25. figs. 7, 8). 



Arachnoidlscus. Fr. single ; v. circular, 

 not undulate, with concentric and 

 radiating lines, and intermediate are- 

 olaB, absent from the centre (pseudo- 

 nodule); marine and fossil (PI. 16, 

 fig. 12), 

 Asterolampra. Fr, single ; v, circidar, 

 finely areolar, except in the centre 

 and on equidistant clear marginal rays 

 radiating from the centre, which is 

 traversed by radiating dark lines 

 (septa) alternating with the marginal 

 rays ; fossil (PI, 25. fig. 5), 



Asterojnphalos. As Asterolampra, but 

 two of the central dark lines parallel, 

 and the corresponding marginal ray 

 obliterated; fossil {PI. 25. fig. 2 ; PI. 

 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 P) areolar lines ; fossil (PL 

 18. fig. 51). 



Odontodiscus. Fr. single, lenticular ; v. 

 covered with puncta (areolae) arranged 

 in radiating rows or excentrically 

 curved lines, and with erect marginal 

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



Oniphalo2)elta. As Actinoptychus, but 

 upper part of margin of valves with a 



few erect spines; fossil (PI, 18. fig. 

 53). 



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. 54,55, 56). _ 



SystepJumia. 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 (PL 18. figs. 57, 58). 

 Coh. 15. AxGULiFER^, Valves angular. 



Amphitetras. Fr. at fh'st miited, after- 

 wards separating into a zigzag chain, 

 rectangidar ; v. rectangular, the an- 

 gles often produced ; marine (PL 16. 

 tig. 9). 



Amphipentas. Fr. solitary ; v, penta- 

 gonal ; fossil (PL 25. fig."^ll). 



Lithodesmium. Fr, united into a straight 

 filament ; v, triangular, one side plane, 

 the others undulate; marine (PL 17, 

 fig. 4). 



Tribe IV, Appendictdatce . Valves mth 

 processes or appendages, or with the angles 

 produced or infiated, 



Coh, 16, Et:podisce.5:, Fr, disk-shaped ; 

 V, circular, 



Eiqmdiscus. 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, 

 \n\\\ a median turgid ring between 

 them=terete Biddulphia; marine.] 

 Coh. 17. BiDDXJLPHiE^. Fr. flattened ; v. 

 elliptical or suborbicular. 



Biddidphia. Fr. rectangular, more or 

 less miited into a continuous or zigzag 

 filament ; the angles inflated or pro- 

 duced into horns ; v. convex, centre 

 usuallv spinous ; marine (PL 16, fig. 

 15 ; PL It), 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). 



Hhizoselenia, Fr. elongate, subcylindri- 

 cal, marked with transverse or spiral 



