824 



SYSTEMATIC HISTOET OP THE INFUSOEIA. 



S. jEfiyptkicus, EM. pi. 33. 1. f. IG. 

 E.irypt. ' Ehreuberg's figure represents 

 the disc witli series of pimcta radiating 

 from the centre, without a distinct um- 

 bilicus, the teeth numerous, subulate, 

 and erect, (v. 69.) 



S. Sinensh, EM. pi. 34. 7. f. 7. Canton. 

 Ehrenberg's figure shows the puncta 

 arranged as in S. JEyijiJtiacus, but the rim 

 striated, and the teeth nodule -like and 

 intra-marginal. 



S. Branmputrce, EM. pi. 35 a. f. 9, 10. 



Ganges. Puncta as in the foregoing 

 species, the rim furnished with short 

 triangidar teeth. 



S._ Niaf/arce (E.). — Frustules small; 

 disc with numerous (often G4) series of 

 punctiform granules radiating from a 

 large granulated umbilicus, and as many 

 acute marginal teeth as rays. EM. 

 pi. 35 a. 7. f. 21, 22. Niagara. This 

 speci(!S is distinguished by its granulated 

 umbilicus. 



Genus PERISTEPHANIA (Ehr.).— Friistiilcs simple, discoid ; disc with 

 decussating parallel series of granules, and numerous marginal teeth. Mari- 

 time. " The characters of this genus so well agree ^^dth Stejihanodiscus that 

 [>erhaps we might more correctly refer the deep-sea form to that genus. But 

 as the hitherto known Stephanodisci are all fluviatile, and the maritime form 

 in the order of its cellules very nearly approaches the purely maritime Cosci- 

 nodiscus lineaius, I have preferred not mixing fluviatile 8tephanodisci T\ith 

 a doubtful maritime form. Perhaps the flow in deep water may have com- 

 mingled a fluviatile form with the maritime ones. Should, therefore, a similar 

 form be hereafter found in any river, this generic name must be cancelled, and 

 the form placed in Stephanodiscus " (EliBA. 1854, p. 230). As we consider 

 iiabitat altogether inadmissible as a generic distinction, we Avoiild distinguish 

 Stcphanodiscus and Peristephania by the radiating granules of the former, 

 and their parallel arrangement in the latter genus. We should prefer to 

 unite this genus with 8ystephania, which diflers only in having intra- mar- 

 gmal teeth. Perhaps even Coscinodisms Vineatus might be included, thus 

 making the parallel arrangement of the granules the essential character. 



Peristephania Entycha (E.). — 

 Habit of Cosciuodiscus Uneatus ] margin 

 of the disc armed with numerous erect, 

 crowded teeth. EM. pi. 35 b. 4. f.^14. 

 Deep soundings of the Atlantic, (v. 73.) 



P. lincata (E.). — Puisembles P. 



Entyclia^ but its teeth are fewer and more 

 distant. EM. pi. 33. 13. f. 22. CaUfomiau 

 deposit and guano. 



In both species the teeth are minute 

 and triangular. 



Genus PYXIDICULA (Ehr.). — Frustules simple or binately conjoined, 

 free or adnate, bivalved ; central portion obsolete ; valves very convex. In 

 Pyxidicula the frustule forms a bivalved box, and differs from CycloteUa in its 

 vaulted valves and the absence of an interstitial portion. The same characters 

 distinguish it from all the Coscinodiscea3. As fii'st constituted by Ehrenberg, 

 Pyxidicula contained very heterogeneous forms ; by the formation, however, 

 of ^lastogonia, Stephanogonia, Stephanopj-xis, and Xanthiop}'xis as distinct 

 genera, this defect has been in a great measiu'e removed ; but we believe it 

 still includes some doubtful species. Dictyopyxis was separated by Ehren- 

 berg, first as a subgenus and afterwards as a genus, for those forms character- 

 ized by the cellulose structure of the valves, lea\-ing in the original genus the 

 smooth and punctated sjiecies. We have thought it more desii^able to regard 

 Dictj'opyxis as a subgenus only, until some of the species are more fnUy 

 known. 



* Frustules smooth or mhmtdy imnctcde. 

 Pyxidicula. 



Pyxidicula opcreulata (E.). — Fru.>- 

 tules small, orbicular, hyaline, punctated. 



EM. pi. 16. 1. f. 46. = P. minor, KSA. 

 p. 21. Fossil, Sweden ; recent, Asia, Eng- 

 land ? Diam. 1-1440" to 1-570". Valves 

 joined by a distinct suture. Kiitzing 

 refers P. "^operadata (E.) to CycloteUa. 



