NEW FORMS OF MARINE DIATOMACE^. 491 



sand. But in the former, a variety of C. Scutellum was figured by mistake : and 

 the latter figure was imperfect, because I had not then seen the faint white bars. 

 This species, along with G. costata, also figured in the third paper alluded to, is so 

 frequent in Lamlash Bay, that I have had ample means of studying it, and am 

 quite satisfied of its being a good species. I may say the same of C. costata, with 

 the remark, that I cannot ascertain from Ehrenberg's figures, whether his Ra- 

 phoneis fasciolata may not be the same form. Ehrenberg's form seems to be 

 much larger, and the markings much coarser and more conspicuous. I must 

 leave this point undecided till I can compare the two forms. 



24. Cocconeis omata, n. sp. PL IX., fig. 24. Form a pure and elegant oval. 

 Length about 0-0022" ; breadth about 0-0014". There is a broad marginal band, 

 marked by strong distant costae, the ends of which are rounded. Within this 

 band the surface appears concave to the median line, which is delicate, with a 

 large, definite, central nodule. The middle part is marked by fainter costae, cor- 

 responding to those on the marginal band, and, like them, so much inclined near the 

 apices, as to be nearly vertical. There is a narrow blank line between the marginal 

 and central costae, and the latter do not reach the median line, leaving a long lan- 

 ceolate blank space in the middle. The whole valve has a rich ornate aspect. 



This beautiful species occurs in Lamlash Bay ; and although scarce as yet, I 

 have been able to examine a sufficient number of specimens to ascertain its cha- 

 racters. I have also observed a few in Loch Fine. 



25. Cocconeis dirupta, n. sp. PL IX., fig. 25. Form a broad, short oval, some- 

 times all but orbicular. Length from 0-001" to 0-0024" ; breadth from 0-0007" to 

 0-0021". Valve thick, and under the half-inch objective of a strong brown colour. 

 Median line irregular, like a slit or tear down the middle of the external surface. 

 The whole valve is marked, except the slit, with coarse, wavy, longitudinal striae ; 

 but, when carefully focussed, fine transverse striae are seen over the whole surface 

 to the median line. Under the half-inch, there is an appearance of a long stauros, 

 which, under a higher power, disappears as such, and can only be seen as a trans- 

 verse gleam of light from below. The striated surface seems to be an outer one, 

 torn asunder in the middle, and from this I have named it. Vertical striae about 

 26, transverse striae about 60 in 0-001". 



I had observed this form in the Glenshira sand, where, however, it was very 

 scarce, and hardly ever entire, so that I postponed its investigation. It occurs 

 very abundantly in Mr Miles's Corallina gathering, and less frequently in several 

 of the dredgings. There is but one known form which is in any degree allied to 

 it. This is C. diaphana, Sm., which I find to occur along with it. After many 

 comparisons, I am disposed to conclude, although these two forms are not the 

 same thing, since C. dirupta is by no means diaphanous, while its striae are con- 

 spicuous and its colour brown, the striae of C. diaphana being very obscure, and 

 the valve colourless, that C. diaphana may perhaps be an imperfect form of 



