488 PROFESSOR GREGORY ON 



slightly expanded at the ends, the angles being bevelled. From the opposite 

 ends the margin inclines very slightly, but visibly, to the middle. Nodules very 

 conspicuous on the F.V., in which the striation also extends, on each side, to 

 rather more than ^th of the width of the frustule, which arises from the convexity 

 of the S.V. 



I first described this species in my first paper on the Glenshira sand, in which 

 the figure was not characteristic. I figured it again in the second paper ; giving, 

 however, a shorter, broader, and constricted form as the type, and the present 

 one as a variety. I have since found it frequent in all the dredgings, but espe- 

 cially abundant in one from Loch Fine, and am now satisfied that the linear form 

 is typical and the broad constricted form a variety. I give the peculiar and 

 characteristic F.V. for the first time. The S.V. in fig. 18 b, is that of a broad in- 

 dividual of the linear type. It is generally narrower, and often even no more 

 than half this width. The shortest specimens are often still narrower. The 

 broad, incurved form, at first regarded as the type, is very scarce in the dredgings, 

 compared to the linear form. 



This form has been supposed to be identical with N. firma, Kiitz, var. (3 ; but 

 its marine habitat at once negatives this supposition ; and, besides, its aspect and 

 colour are quite different. N. firma is brown, while N. maxima is of a pale straw- 

 colour. The striation in N. firma is coarser and more conspicuous; and, lastly, 

 N. firma is broader, has acute extremities, and yields several marked varieties, 

 such as Ehrenberg's N. dilatata and N. Amphigomphus ; while the only observable 

 variety of N. maxima is the shorter, broader, incurved one, represented in fig. 2 

 of my second paper on the Glenshira sand. 



19. Pinnularia (?) subtilis, n. sp. PI. IX., fig. 19. Form linear rhombic, very 

 narrow, with elongated apices. Length about 0035" ; greatest breadth about 

 0-00025". Nodule definite. Costae about 28 or 30 in 0001"; transverse, slightly 

 inclined towards the apices. 



This form occurs in Lamlash Bay. I do not feel quite sure about its genus. 

 It may be a Navicula. The whole form is delicate and translucent, and it is far 

 from conspicuous. 



20. Pinnularia rostellata, n. sp. PI. IX., fig. 20. Form linear, broad, with 

 acuminate ends, terminating in short, acute apiculi. Length from 0'002" to 

 00027"; breadth about 0007". Central nodule definite. Costse strong, subdis- 

 tant, inclined near the ends, reaching the median line, about 14 in 0-001". 



This pretty form occurs both in Lamlash Bay and in Loch Fine. It is not 

 frequent, but I have been able to examine a considerable number of specimens, 

 which are quite constant in their character. 



21. Pinnularia Allmaniana. PI. IX., fig. 21. Form elliptic-lanceolate, broad, 

 extremities subacute. Valve highly convex on one side, concave on the other. 

 Length from 0-0016" to 0-0026" ; breadth from 0-001" to 00014". Costa? appa- 



