936 



SYSTEMATIC HISTOEY OF THE INFUSOEIA. 



ginal cell has 2 opposite teeth, whicli 

 constrict it. 1-372". Fossil. Sicily. 



D. bqmrtita(E.). — Resembles D. Cmx, 

 but has 2 minute cells in the centre. 

 1-504". Fossil. Oran and Sicily. 



D. superstructa (E.). — Spines 4; cells 

 9, 4 marginal. 1-600". Fossil. Sicily. 



3* Spines 6 (2 usually longer). 



D. hitemaria (E.). — Cells Q, aU mar- 

 ginal, the 3 largest next each other. 

 1-432". Antarctic Ocean. 



D. Hexathyra (E.).— Cells Q, 5 mar- 

 ginal and 1 central. 1-864. Fossil. 

 Sicily. 



J)^ Speculum (E.). — Six unamied cells 

 round a central one. Common, both 

 recent and fossil. 1-860". (xn. 62, 63.) 



D. gracilis (K.). — Resembles D. Sp>e- 

 culum ; but the spines are elongated and 

 slender. Recent. 



D. diommata (E.). — Six unarmed cells 

 round 2 central ones. 1-660". Fossil. 

 Virginia. 



D. aculeata (E.). — Resembles D. Spe- 

 culum; but each marginal cell bears a 

 tooth. Common, both recent and fossil. 



D. Binoculus (E.). — Resembles D. 

 aculeata, but has 2 minute ceUs in the 

 centre. 1-444". Fossil, ^gina. 



D. libera (E.). — Cells unarmed, 7 mar- 

 ginal and 2 central. 1-600". Maryland. 



1). triommata (E,). — Cells unarmed, 

 6 marginal and 3 central. 1-864". 

 Virginia. 



D. Haliomma (E.).— Cells 10, 7 mar- 

 ginal and 3 central. 1-840". Oran. 



D. liemisplicerica (E.). — Hemispherical, 

 6-spined ; 1 2 cells, in two circles, round 

 a. central one ; the inferior apertm^e half 

 closed by 6 marginal teeth. 1-744". 

 Bermuda. D. triommata and J), diom- 

 7nata resemble, in their turgid habit, 

 this species. 



4* Spines more than 6. 

 D, septenaria (E.). — Spines 7; cells 



unarmed, 7 marginal and 1 central. 

 1-864". Oran. 



D. Ornamentum (E.). — Resembles D. 

 septenaria ; but each marginal cell bears 

 a tooth. 1-444". Fossil. Sicily. 



D. heptacanthus (E,). — Spines 7 ; cells 

 13, 7 of them marginal. 1-552". Fossil. 

 Greece. 



D. octonaria (E.). — Habit of D. Orna- 

 mentum, with 8 spines; marginal cells 

 iiTegular, fewer in number at that part 

 where the spines are increased, and with 

 a very large centi*al cell. 1-1152" ex- 

 clusive of spines. Perhaps a monstrous 

 variety of D. Ornamentum. 



D. Stauracanthus (E.). — Eight-spined ; 

 4 marginal, dentate cells, roimd a centi'al 

 one. 1-648". Fossil. America. 



B.polyactis (E.).— Rays 9 or 10; 10 

 marginal cells and 1 central, arranged in 

 a reticulate steUate fonn. In chalk-marl. 



5* Pentagojial ; angles acute, hut not 

 spinous. 



D. elegans. — Pentagonal, perforated by 

 numerous small ceUs and 7 central large 

 ones, of which one occupies the centre. 

 1-912". Fossil. Caltanisetta, Sicily. 



Doubtful or obscure Species. 



D. Navicula (E.). — Cells 8 ; figm-e ob- 

 long, obtuse, cylindrical, reticular, -udth 

 a median septum like a Na^dcula. Fossil 

 in chalk marl. Ehrenberg's figure re- 

 sembles D. Ponticidus. 



D. ? sple?idens (E.). — Oblong, tabular, 

 with dentate apertm-es (cells), 13 in 

 number. If it be calcareous, it is similar 

 to Coniopelta. 



D. anacantha (E.). — Resembles D. 

 Speculum, with obsolete spines. EB. 

 1854, p. 238. North America. Perhaps 

 a variety. 



D. JErebi (E.). — Resembles D. Specu- 

 lum, with small, subequal spines ; walls 

 of the cells thin. E. I. c. North America. 

 A doubtful species ; perhaps a variety. 



Genus MESOCENA (E.). — Frustules free, each forming a ring, which is 

 mostly margined with spines or teeth. Mesocena resembles Bictyocha, but is 

 destitute of its central reticulation. 



Mesocena heptagona (E.). — Frustules 

 annular, wdth 7 external teeth. EM. 

 pi. 20. 1. f. 49. (xii. 71.) Actiniscus ?, 

 E. Peru. 



M. octogona (E.). — Frustules annular, 

 with 8 external teeth. Peru. As this 

 form differs from M. heptagona merely 

 by its additional tooth, it is probably a 

 variety. 



M. bisoctonaria (E.). — Frustules annu- 

 lar, with 8 external teeth, and as many 

 internal ones alternating with them. 

 = M. bioctonaria, KA. p. 142 ; EM. 

 pi. 35 A. 18. f. 10. In Peruvian guano. 



M. binonaria (E.). — Frustules annidar, 

 with 9 external teeth, and as many 

 internal ones alternating with them. 

 EM. pi. 35 A. 18. f. 9. In Peruvian 



