NEW FORMS OF DIATOMACE^. 485 



middle, the two halves broad and rounded, with subacute extremities. Median 

 line broad; central nodule square, definite. Length about 0045"; greatest 

 breadth O^OOIS". Striation coarse, strongly moniliform, not reaching the median 

 line, but leaving a narrow blank space on each side of it. Striae about 18 in 

 0001, much inclined near the apices. 



This form, which I had found frequent in the Glenshira sand, is also fre- 

 quent in the new dredgings. It is regarded by many as a variety of N. didyma, 

 and by others as a variety of N. Crabro. I am disposed to consider it a distinct 

 species, on account of its peculiar and very constant form, and also because it has 

 a decided light-brown colour in balsam, under a low power, which N. didyma has* 

 not. It is much larger than N. didyma. As to N. Crabro, the moniliform structure 

 in it is always obscure, and the form is also different. I cannot perceive that A". 

 Bombus passes into either of these species by intermediate forms. But whatever 

 be the ultimate decision on this point, I give it here.as the form called by Ehren- 

 berg N. Bombus ; which, be it species or variety, is at all events conspicuous, and 

 very constant in its characters. 



In my last paper on the Glenshira sand, I have figured several Naviculse and 

 Pinnularise of the panduriform group, and I have pointed out that this remark- 

 able group requires thorough investigation. In order to contribute towards this 

 end, I have figured the present form, as well as N. Musca, a new member of the 

 same group ; and I shall describe, farther on, another, namely a remarkable form 

 of Pinnularia Pandura, Breb. 



13. Namcula Lyra, Ehr. PI. IX., fig. 13 and 13 b. Form oblong-elliptic, broad ; 

 often contracted to short produced extremities. Length from - 002" to 0"0045" ; 

 breadth 0-0007" to 00018". Median line fine, interrupted by a large indefinite no- 

 dule, extending transversely. On each side of, and in contact with, the median 

 line, is a linear, somewhat broad, striated band, and this is separated from the very 

 broad, marginal, striated band by a narrow linear blank space. These linear blank 

 spaces are, in each half, united by their base to the extremities of the nodular 

 blank. They bend outwards from this point, then inwards, and finally again 

 outwards at their extremities, thus forming, in the entire valve, two lyrate shapes 

 united by their bases. Hence the name. The lyrate character is often much 

 more decided than in the specimens figured. The extremities of these lyrate 

 blanks generally reach the margin of the valve near its apices, but sometimes 

 fall short of this, as in the figure. Striae about 22 or 24 in 0001', somewhat in- 

 clined near the apices. 



This species, which occurs in the Glenshira sand, and is scattered through all 

 the dredgings here mentioned, has been described, though not as I have described 

 it above, in the 2d volume of Professor Smith's Synopsis. Professor Smith seems 

 to have seen only a variety, to be presently mentioned, which does not possess the 

 lyrate character, and has therefore omitted that character. He refers to a figure 



VOL. XXI. PART IV. 6 P 



