OF THE CH.ETOCEEE.^. 



865 



Genus OMPHALOTHECA (Ehr.).— Characters unknown to us. Judging 

 from Ehrenberg's figure of the only species, it seems scarcely distinct from 

 Goniothecium. 



Omphalotheca hispida, EM. pi. 35 a. 

 9. f. 4*. Ganges. The figure apparently 

 represents a frustule in the process of 

 division. The valves are unequal j the 



smaller one smooth, the larger some- 

 what conical and furnished with scat- 

 tered spines ; connecting-zone slightly 

 produced beyond the valves, (vin. 44.) 



Genus PERIPTERA (Ehr.). — Frustules simple, compressed, unequally 

 bivalved ; valves simple, continuous, not cellulose ; one valve naked, turgid, 

 the other winged or horned ; horns affixed to the extreme margin, sometimes 

 branched. Approaches very near to Syndendrium and Dicladia. We think 

 these three genera might be united with advantage. 



Pemptera tetracladia (E.), — Smooth, 

 almost navicular; one valve with four 

 equidistant spines, branched at the apex, 

 the other simple. EM. pi. 33. 18. f 9. 

 Fossil. Bermuda deposit. Diam. 1-1440", 

 including spines 1-864". Without the 

 spines, it resembles an Amphora. (yi. 30.) 



P. cJilamiclophora (E.). — Smooth, al- 

 most navicular; one valve at the side 

 plane and surmounted by a finel^^-nerved 

 membrane, the other turgid at the mid- 

 dle, unarmed. EM. pi. 18. f. 98. Fossil. 

 Bermuda, (viii. 25.) 



Genus RHIZOSOLENIA (Ehr.). — Filamentous; frustules subcylindrical, 

 greatly elongated, silicious, annulate ; annuli broadly cuneate ; surface stri- 

 ated, extremities calyptriform, pointed with a bristle. This genus was con- 

 stituted by Ehrenberg for the reception of certain silicious organisms found 

 in guano and various fossil deposits. The characters assigned by him to this 

 genus are, " lorica tubular, with one extremity round and closed, while the 

 other is attenuate and multifid, as if terminating in little roots." The dis- 

 covery of this remarkable genus in a living state has, we believe, proved that 

 the species described by Ehrenberg are only fragments of forms similar to 

 those we are about to describe. Professor Schultze has detected in R. styli- 

 formis and R. ccdcar-avis a circulation of minute granules analogous to the 

 currents observed in the hairs on the filaments of Traclescantia procuynbens. 

 (Schultze, MJ. vii. p. 16.) 



Rhizosolenia styliformis (Bri.). — 

 Frustules from 6 to 20 times as long as 

 broad; transverse lines (annidi) distinct ; 

 sm-face striated, striae oblique, about 40 in 

 ■001", terminal process at the base spatu- 

 late and bifid. Found in Noctilucae, Yar- 

 mouth ; stomachs of Ascidians, York- 

 shire ; Salpse, Atlantic. Bri M J. vi. p. 94, 

 pi. 5. f. 5 ; Norman, ANH. xx. p. 158 ; 

 Prof. Schultze, MJ. vii. p. 18. pi. 2. f. 1. 

 (Am. 32.) From the elongated base of 

 the calyptriform process a stout line or 

 rib runs up on either side to nearly the 

 apex of the cone ; at base of the lines a 

 small horn, slightly cm-ved towards the 

 annuli, is frequently to be detected. 

 Self-division has been observed in this 

 and some of the following species. 



R. imhricata (Bri.). — Frustules 4 to 

 7 times as long as broad, annuli di- 

 stinct, sm'face of valve coarsely punctate, 

 terminal process subulate, entire. Found 

 with the preceding species. Bri MJ. 



p. 94, pi. 5. f 6. The direction of the 

 transverse lines (annuli) and puncta 

 give this species an imbricated appear- 

 ance. 



R. setigera (Bri.). — Frustules 5 to 15 

 times as long as broad, annuli obscure, 

 striae very faint, terminal bristle fre- 

 quently as long as the colom-less frustule. 

 In Noctilucae, Ascidians, and Salpae. 

 Bri. /. c. p. 96, pi. 5. f. 7. (\^I. 33.) This 

 species is remarkable for the great length 

 of the terminal bristle and its extreme 

 delicacy. 



R. alata (Bri.). — Annuli distinct, striae 

 faint, terminal process alate, recm'ved, 

 blunt. In Ascidians, Yorkshire. Bri. /. c, 

 p. 95, pi. 5, f 8. This curious little spe- 

 cies is distinguished by its small but 

 conspicuous setae attached to the base of 

 the calyptriform process. 



R. calcar-avis (Schultze). — Frustules 

 small, annuli indistinct ; tenninal process 

 slightlv sigmoid, the point resembling 

 3 K 



