524 PROFESSOR GREGORY ON 



is transversely striated ; but the striae cannot be traced throughout without alter- 

 ing the focus. Striae about 38 in 0001 ". 



This remarkable form was first described by De Brebisson as occurring near 

 Cherbourg. No form is better adapted to show the structure of a complex Am- 

 phora, on account of its transparency, and the breadth of the convergent bars. 

 I have found it in Lamlash Bay, where it is not very frequent ; and also sparingly 

 in Loch Fine. No detached segments have yet occurred. 



93. Amphora acuta, n. sp, PL XIV., figs. 93 and 93 6. Form of detached 

 segment arcuate, dorsal margin convex ; in some examples with a slight inflec- 

 tion just before the extremities; ventral margin straight, or slightly concave, 

 ends acute. The inner lines are very near the ventral margin, and almost ex- 

 actly parallel to it, but sometimes a little incurved, except in the middle, 

 where the nodule meets them. Nodule elongated into a strong transverse 

 bar. Length of segment 0-0035" to 0-0055"; breadth of it 0-00075". The seg- 

 ments are marked by transverse striae, about 36 in 0-001", which are distinctly 

 moniliform. 



I have not yet seen the entire frustule ; but it is no doubt complex, for I found 

 a good many half-frustules, as it were, formed of segments lying one over the 

 other, to the extent of five or six. Sometimes no cross bar is seen, probably be- 

 cause the cross bar is only found on the lateral segments, which may have be- 

 come detached, and left the middle ones by themselves. One figure shows a group 

 or pack of segments. 



This species occurs in Lamlash Bay, but is more frequent in Loch Fine. It 

 is probable that the entire frustule will somewhat resemble A . nobilis in form, 

 but not in its hyaline aspect. On comparing the segments of A. acuta with those 

 of A. nobilis, as seen in the entire frustule, the curve lines in the latter are seen 

 to be very deeply curved, and to be much farther from the inner margin of the 

 segment, whereas the inner lines in the segments of A. acuta are straight, or very 

 nearly so, and close to the ventral margin. In A. acuta, the striae, though not 

 coarse, are strongly moniliform, while the striae of A. nobilis are much finer. Yet 

 it is probable that these two species are related. 



(I have very recently observed two specimens, apparently of A. acuta, in which 

 two segments are placed opposite, and close to each other. I suppose this vieAv 

 to represent the flat side of the frustule, or the half frustule, like a cut orange, as 

 in the figure of A. Grevilliana, fig. 89. But in these specimens of A. acuta, the 

 two lateral segments are in apposition.) 



94. Amphora crassa, Greg. PI. XIV., figs. 94, 94 b, 94 c, 94 d. Form of frus- 

 tule rectangular, broad, with rounded ends. Length from 0-0025" to 0-004"; 

 breadth from 0-0008" to 0-0013". Lateral segments linear, from 0-0005" to 0-00075" 

 in breadth, straight, or very slightly incurved on the dorsal margin, which, at 

 the apices, bends inwards, forming short, rounded beaks. Sometimes, as in one 



