138 W. B. TUEHEK, FKKSH-WATER ALGJE OF EAST INDIA. 



Gen. 21. Onychonema, Wallicii. 



(Desm. Bens:, in Armals X. H. p. 194, 1860; Xanthidiastrum, Delp. Desm. Sub. Alp. p. i»8, 18715). Filainenta 



com pressa, marginibus incisa; lateribus cellularum aut rotuadatis ve] serratis; froudes profunde coustrictae, pro- 



cessubus vel cornubus sub-capitatis divergentibus alternatira positis conjunctae, G. C. W. emend. 



1. O. unciiintiiiii. Wallicii (1. c. p. 195, t. \ III, f. 7—11; Mac*. Nos. 40, 44, 45). O. 

 eellulis a fronte visis quadrangularibus, profunde constriotia; semicellulis apice cornua 

 2 oblique posita ferentibus, utroqué latere uneinulis singulis incurvis prseditis; angulis 

 superioribua 2—3 dentato-sefratiSi rotundatis; apicibua et Lateribus punetatis; sinn pro- 

 fundo sub-lineari extrorsum ampliato; centrali parte frondis lsevi. A latere visum bi- 

 globulatum parum et rotundate eonstrictum, cornubus divergentibus; a vertiee visum 

 ellipticuBQ apicdbua acutum, dorso lineis rectis 2 punctorUm (granulorum.?) ornatum. 

 Walt.ICH remarks in Beng* Desm.: »The joints in this turin are somewhat more turgid 

 than in Sphcerozosma or Lewonema (Spondylosium), The constriction is so deep as 

 to leave liitle more than a third of the entire breadth of the joint as a connecting 

 isthmus. The segment- are closely approximate. The cornua are situated obliquelv 

 tu each other, at the outer thirds of the lateral (apical) aurfaces; they are cylindrieal, 

 halt' as long as the segments are broad, and slightly capitate. Between the cornua 

 aml the claw-like processes a row of minute teeth presents itself, whilst the median 

 line of the segments, on their outer aspects, is bordered l>v two fows of minute puncta. 

 These are, however, rarely \ i^il^l* 1 . except in such joints as happen to be emptv. The 

 wbole of the cornua (as seen in the front view) plaeed on the same side of the median 

 line and same extremity of the segments, overlap the adjoining joint in the same di- 

 rection. The two sets of cornua, therefore, as seen in this view, face in opposite 

 directions, the upper in one, the lower in another. These cornua are not mere tuber- 

 cular solid excrescences, as in Sphcerozosma, but are formed by an extension of the 

 cell-walls, like the lingers of a giove, and are accordingly hollow for a eertain distance, 

 the tenacity of the lilainent being st) far increased by their instrumcntality that it is 

 constantlv seen to divide rather at the segments than at the joints. 



In the yoUng state, the uncinate processes are sometimes imperfectly develo- 

 ped, and might induce the belief, that the form exhibiting them in this state W&s a 

 variety. 



The marginal view (of the filament) is linear, and faintly sinuate or incised, 

 from the outline of the cornua being observable, and the constriction, which in this 

 a-pect is just discernible. In the end view, the alternating and divergent eharacter 

 of the eornua is very remarkable. The last feature affords a close point of resem- 

 blance, it may be observed, to the strueture and apparent function of the obliquely 

 arranged spines and cornua in some species of the genus Biddulphia (Diatomaceae) : < i. 

 C W. p. 195. 1. c. 



Long. 18 — 20, lat. s. unc. 24 — 30, lat. isth. 5.5 — 8, crass. 11 — 12.5, long. unc. 

 3.5 — 4.5, long. corn. G — 7 fi. Wallich gives long. 20 — 30.5, lat. 30.5 — 51 ,u (unc. et 

 corn. includ.?). 



Forma ft teuuis n. f. 



