NEW FORMS OF MARINE DIATOMACE.E. 507 



of the valve, in a narrow, elongated nodule, which is in a line with the terminal 

 nodules, also long and narrow. But close to the outer margin, at the constric- 

 tion, is another large round nodule. The narrow portions, which lie between 

 the curve-lines just mentioned and the inner margin of the valve, appear, like 

 the middle space, to be unstriated ; but perhaps this is because they lie in a 

 different plane from the outer compartments. And even in the last, the striae are 

 too fine to be resolved under a power of 400. 



This remarkable form occurs in one of the Loch Fine dredgings, where, how- 

 ever, it is very scarce. I have not yet recognised with certainty the S.V., but 

 there are some forms which may prove to belong to it. 



61. Amphipivra maxima, n. sp. Plate XII., figs. 61 and 61 b. Form of F.V. 

 rectangular, very broad, but deeply constricted in the middle, and rounded on the 

 ends. Length 00068'' ; greatest breadth 0-0028" to 0-003", breadth of frustule at 

 constriction 0-0017'. Central nodules large, situated close to the constriction in 

 the outer margin. Terminal nodules on the inner margin of valves, conspicuous. 

 Over each valve lies a strong, broad plate, arcuate outwards, straight on its inner 

 margin, which coincides with that of the valve. Outer margin of plate prominent 

 in the middle, and on each side of this prominence slightly incurved ; thick, over- 

 lapping the valve at the constriction. Breadth from the margin of one plate at 

 this point to that of the other 0*0023". Valves and plates transversely striated. 

 Striae distinct, parallel, about 36 in 0-001", thicker and apparently coarser at the 

 margin of the plate. S.V. lanceolate, ends acute, with a trace of a constriction just 

 before the apices. Greatest breadth 0-00125". Two strong lines, as in Apr. lepi- 

 doptera, proceed from the apices, on one side, and curve inwards to join a large 

 nodule at one-third of the width. Round this nodule the striae are curved, as if 

 pushed outwards. Between the nodule and the nearest margin the striae are very 

 short, and they leave a large blank space, extending to the margin. Valve thick and 

 very convex on the S.V. Query, Are the curve-lines on the S.V., the outer margin 

 of the plates, seen on the F.V ? From the convexity of the S.V. its striation is more 

 conspicuous than that of the F.V. 



This, which is one of the finest and most interesting forms described in this 

 paper, first attracted my attention in the Glenshira Sand. But I could only find 

 there halves of the F.V ; and I postponed the description of it. In Professor All- 

 man's Lamlash Bay dredging I again saw these halves occasionally ; but it was 

 not till I examined, in October last, the Loch Fine dredgings, that I found, in one 

 of them, besides a number of the same halves, some entire frustules ; and finally, 

 the S.V. which, from its comparative narrowness, is seldom presented ; the frus- 

 tule or detached valve lying on its broadest side. There is something very beauti- 

 ful in the entire form ; and in its structure it is peculiarly interesting, as present- 

 ing the peculiar lateral plates, already noticed in Apr. pusilla, Apr. plicata, and 

 Apr. lepidoptera, and that in a high degree of development. The occurrence of 



