522 PROFESSOR GREGORY ON 



teral segments arcuate, ends acute, inner curve-lines strongly curved, nodule 

 elongated into a transverse bar. The converging bars in the middle are numerous, 

 in apposition, and the whole frustule very hyaline. It is marked by fine trans- 

 verse striae, easily seen on the lateral segments, and which may also be traced, by 

 careful manipulation, across the whole frustule. Striae about 40 in 0-001". 



I first observed this fine and conspicuous form in the Glenshira Sand, but 

 postponed the description of it that I might examine it farther. I have found it 

 more frequently in Lamlash Bay and in Loch Fine. 



88. Amphora Arcus, Greg. PI. XIII., fig. 88. Form of entire frustule barrel- 

 shaped, ends truncate. Segments arcuate, sub-apiculate, marked by coarse moni- 

 liform striae, which are also seen over the entire form. Length from 0-0035" to 

 0-0045" ; breadth about 0002." Striae 16 or 18 in 0-001". The longitudinal bars 

 in the middle between the lateral segments are about 16 or 17, closely set, and we 

 can see that they are segments seen edgewise. 



This fine form was rather frequent in the Glenshira Sand, but was only then 

 known in the shape of detached segments, two of which I figured in my first paper 

 on that deposit (Mic. Jour., vol. iii., pi. iv., fig. 4), without at that time under- 

 standing its real structure. Subsequently I recognised the entire frustule in the 

 Glenshira Sand, and also in the dredgings from Lamlash Bay. In my third paper 

 I figured an imperfect specimen (Trans. Mic. Soc, vol. v., pi. i., fig. 37), and I now 

 give a more perfect one, which shows that it really belongs to the complex group. 

 See fig. 88. 



89. Amphora Grezilliana, Greg. PI. XIII., fig. 89. Form of entire frustule 

 nearly oval, broad, slightly truncate at the extremities, which are broad, the line 

 joining the apices of the lateral segments being concave, so that a short process 

 stands out at each side. Length about 0-006" ; breadth about 0-002". In the spe- 

 cimen figured (fig. 89 ) the form of the lateral segments is perfectly seen, probably 

 because the frustule is viewed from the flat side, as we view an orange cut in 

 half from the cut side. These segments are precisely like that figured in my last 

 plate from the Glenshira Sand (Trans. Mic. Soc, vol. v., pi. i., fig. 36*). They 

 are broad, arcuate, with somewhat acute rostra, and three curve-lines on their 

 surface, which are peculiar to this species. They are marked with strong trans- 

 verse moniliform striae. Striae about 28 in 0*001". Between the lateral segments 

 are five or six convergent bars, which are the backs of other segments, and which 

 are in apposition, except at the ends, where they diverge a little, from their 

 apices becoming suddenly narrower. 



This fine species occurs both in the Glenshira Sand and Lamlash Bay. But 

 the entire frustule given under this name in the plate just referred to (at fig. 36) 

 does not belong to this species, as may be seen at once by comparing it with fig. 

 89, and by the form of its segments, as seen in that figure. The segment in that 

 plate, fig. 36*, is correct, as above stated. 



