14 JOHNSTON, ON DIATOM ACK.E. 



Centre smooth; the surface of the disc presents alternating 

 ■wedge-shaped elevations (rays) and depressions, which 

 originate at the centre, the former pointedly; on each ray 

 there proceeds from a marginal nodule a delicate acicular 

 rib, which terminates apicially near the umbilicus, and in 

 the middle of each depression a delicate line. Very faint 

 indications of reticulation just within the margin. The 

 whole surface, exclusive of the centre, covered with extremely 

 minute quincuncially arranged puncta ; and at the margin an 

 encompassing row of fine granules. Colour very pale straw. 

 Diameter T 4Y' to 23V- 



In Elide guano. 



In my specimens the rays are twelve in number. 



Arachnoidiscus, Ehr. 



A valve of Arachnoidiscus was found, which is interesting 

 as a variety of that genus, if it have not distinctive specific 

 characters. The centre is clear, immediately surrounded by 

 irregularly disposed granules, larger than those on the 

 general surface. In the same guano I found a number of 

 frustules, not distinguishable from A. japonicus, having 

 regular central rays, which is not the case with the one I 

 have delineated. Diameter s\-^". 



In Elide guano. 



ACHNANTHES, BoriJ. 



A. angustata, Greville (?) — Front view. — Much bent. 

 Transversely banded, bands resolvable into dots, 26 in 0-001". 

 Half of the hoop transversely striated. A row of granules 

 along the base of each frustule, those of the upper one being 

 very fine. An apparent aperture (not an opening) at the 

 inferior extremities of the under valve. Length yir"' 



Side view. — Both valves elongated, slightly swollen in the 

 middle, and with rounded extremities. Transversely banded, 

 the striae being rows of dots, interrupted by a line near to 

 and parallel with the margin. Externally the striai arc 

 alternately swollen, giving the appearance shown in the 

 figure. Upper valve traversed by a central longitudinal 

 row of puncta, around which, at the extremities, the stria; 

 are radiate. Lower valve similarly divided, but the ex- 

 tremities, instead of being entire, appear to be Largely per- 

 forated ; in the clear space a cresccntic line. "Width -fl?". 

 (Fig. 13 a, />,/.) 



In Elide guano. 



This species presents a striking contrast with the following. 



