OF THE COSCINODISCE.E. 



833 



Cellules 12 in 1-1152". Diam. 1-348". 

 The spines are far more numerous and the 

 cellules less distinct than in S. aculeata. 



S. Diadema (E.). — Disc densely cellu- 

 lose ; spines numerous, marginal, in- 

 cm-ved, conjoined at their extremities 



by a membrane. EM. pi. 33. 18. f. 11. 



Bermuda. Cellules 14 in 1-1152". Diam. 

 1-864". Much smaller than the two 

 preceding species. All have a variable 

 number of teeth. 



Genus SYMBOLOPHORA (Ehr.). — rmstules orbicular, not concatenate; 

 disc with striae or dotted lines, radiating from a solid angular centre. Sym- 

 Ijolophora differs from Actinocyclus in having an angular or steUate hyaline 

 centre. 



Ehrenberg has placed in this genus forms which agree only in their hyaline 

 angular umbilicus ; and the species with radiating series of dots scarcely 

 differ from Coscinodiscus. 



Symbolophotia Trinitatis (E.). — Disc 

 having a triangular crystalline umbilicus 

 with a crenated margin, from which 

 radiate six fascicles of very fine lines 

 diverging towards the margin. EB. 

 1844, p. 88. (XI. 36.) Fossil. Maryland. 

 We believe no one except Ehrenberg 

 has observed this species, for which the 

 genus was constituted ; and it has been 

 suggested that his figure may represent 

 what he erroneously supposed to be the 

 original form (as shown by a fragment) 

 of Triceratimn Marylandka ; but in this 

 opinion we cannot concur, because in 

 several instances where Ehrenberg has 

 founded species on mere fraginents he 

 has figiu'ed the fragments as he observed 



; them, Mdthout attempting a restoration 



i of their supposed entire figm-e. 



I S. acutangida (E.). — Resembles the 



I preceding in size and habit, but has the 



i angles of its umbilicus acute. EB. 1845, 



i p. 81. Fossil. Virginia. 



1 S. ? Microtrias (E.). — Disc tm-gid, 



I with a stellate umbilicus, from which 



radiate series of pimcta. Antarctic Ocean. 



Umbilicus triradiate = S. 3Iicrotnas, E. 



/. c. 1844, p. 205 ; EM. pi. 35 a. 21. f. 16. 



Umbilicus cruciate or fom'-rayed = S. 



Tetras, E. I. c. Umbilicus five-rayed = /SI 



Pentas, EM. pi. 35 a. 22. f. 19. Umbilicus 



six-rayed = S. Hexas, E. I. c. This species 



differs from a Coscinodiscus only in the 



presence of the stellate umbilicus. 



Genus HETEE,0STEPHA:NTA (Ehr.).— Characters lmkno^vn to us. 



Heteeostephania RotJiii, EM. pi. 

 35 A. 13 B. f. 4, 5. (v. 85.) _ Elbe. Disc 

 with radiating series of minute puncta. 



8 or 10 marginal teeth or minute pro- 

 cesses, and no umbilicus. Front view 

 with minute, erect, marginal teeth. 



Genus HALION'YX (Ehr.). — Frustules orbicular, not concatenate; disc 

 rayed ; number of rays definite, not starting from the umbilicus ; no internal 

 septa. It resembles Actinocyclus, except in its umbilicus not being radiate ; 

 or, in other words, its central ocellus is wanting. In Hke manner Coscino- 

 discus differs from Symbolophora in its non-radiate umbilicus, which is a 

 simple void space. 



Halionyx senarius (E.). — Surface of 

 disc wdth six rays ; each compartment 

 is marked by parallel lines, which de- 

 crease by equal gradations on either side 

 of a radiating median line ; loosely and 

 widely cellulose ; umbilicus entire, punc- 

 tated. KA. p. 130. Antarctic Ocean. 

 Diam. 1-720". Approaches Actmoptychus 

 undulatus. 



H. undenarius (E.). — Disc with eleven 

 or twelve rays ; umbilicus large, punc- 

 tated, not radiant, (v. 82.) EM. pi 35 a. 

 21. f. 12. = ^. duodenarius, E. olim. Ant- 

 arctic Ocean. Diam. 1-576". Ehrenberg'a 

 figure shows the disc with a granulated 

 centre, from which proceed radiating 

 series of puncta and eleven darker or 

 shade -like rays. 



Genus ACTINOCYCLUS (Ehr.). — Frustules simple, disciform; disc mi- 

 nutely and densely punctated or cellulose, generally divided by radiating single 

 or double dotted lines, and having a small circular hyaline intramarginal 

 pseudo-nodule. We consider Actinocyclus, as limited by Ehrenberg, a well- 



3h 



