NEW FORMS OF MARINE DIATOMACEiE. 489 



rently marginal, strong, about 20 in 0001", giving the appearance of a narrow 

 marginal band of very strong costse. Within this band, however, the valve, on 

 close inspection, is found to be marked with similar but much fainter costse 

 nearly to the median line. The valve appears to be thicker near the margin than 

 in the middle, and this perhaps is the reason why the costse are so strong and 

 conspicuous there. 



This form is frequent in Professor Allman's dredging from Lamlash Bay, and 

 it occurs also in Loch Fine. I have named it after Professor Allman, to whom I 

 am indebted for this dredging, the richest of all those here described. 



22. Pinnularia Pandura— Navicula Pandura, Breb., var. /?, elongata. PI. IX., 

 fig. 22. Form deeply constricted in the middle, with elongated sub-triangular 

 ends, and obtuse apices. Length 0-0075" or more ; greatest breadth 0-002", breadth 

 at constriction 0-0014". Median line sharply defined, broader at the centre than 

 at the ends ; nodule square, definite. On each side of the median line, and a 

 little way from it, there is on each side a line or ridge, apparently formed of large 

 granules, but probably only apparently so, from the sudden and sharp elevation 

 of the ends of the costse. Costse, from this point to the margin, perfectly entire 

 and glassy, like those of P. alpina. Valve thick, costse 10 or 11 in 0001", some- 

 what inclined near the apices. 



This seems to be a variety of De Brebisson's Navicida Pandura, which I have 

 represented in the second paper on the Glenshira sand, in figs. 11, 12, and 12*. 

 But as De Brebisson himself describes the costse as being entire, and represents 

 them distinctly so in his figure of the species, I have changed the generic name to 

 Pinnularia. I consider it as quite distinct from N. Crabro, Ehr., as described by 

 Professor Smith, in vol. ii., of the Synopsis ; for the latter has obscurely monili- 

 form striee, as is shown in Dr Greville's figure of it from Trinidad, in the Micro- 

 scopical Journal for January 1857. 



The forms represented in figs. 11, 12, and 12* of my second paper on Glenshira 

 {Micr. Trans, iv., pi. v.), and that here figured (fig. 22), are abundant in several 

 of the dredgings ; but of all the numerous examples I have examined, not one 

 exhibits the slightest trace of moniliform structure ; and I have had the satisfac- 

 tion of having this observation confirmed by Dr Greville, who is acquainted with 

 the form in which that structure exists obscurely. Unless, therefore, we are pre- 

 pared to abolish the distinction between entire and moniliform striation, on which 

 Professor Smith founds the distinction between his genera Navicula and Pinnu- 

 laria, we cannot regard this form as a Navicula. 



VOL. XXI. PART IV. 6 Q 



