A RARE BRITISH DIATOM. 37 



any species of AmpMpleura. From any Cymbella or Ceratoneis, 

 both of wliicli it more closely resembles, it differs in having a 

 complex girdle, and from the latter genus also by the possession 

 of a true, although very faint, raphe. From any of the fore- 

 going genera it differs also in having the ventral side of the 

 frustule slightly narrower than the dorsal side. It is no 

 Epithemia, as one correspondent suggests, because, among 

 other reasons, there are no transverse ribs alternating with 

 delicate rows of punctae. It differs in appearance from the more 

 usual outline of the 220 known forms of Amphora by the high 

 proportion of its breadth-length ratio, which, however, is not a 

 character of generic value. Being a true Amphora the estab- 

 lishment for its reception of the genus Okedenia is opposed 

 to the laws of scientific nomenclature and cannot be maintained. 

 It therefore follows that the latter name must be regarded as 

 a synonym, and the excellent Mr. Okeden commemorated in 

 some other way. 



So far as I can glean, "D. G," is the first diatomist to have 

 found this rare species on the coast of England or Wales since 

 the time of Ralfs, or for more than sixty years. As this species 

 has never been adequately described or figured, and as " D. G." 

 has kindly supplied me with a sample of a fresh gathering 

 which he has fortunately obtained, I readily comply with his 

 request that I should describe and figure it. 



Description. — Valve sub-linear, arcuate, a little flattened at 

 the middle on the dorsal side, and often slightly tumid about 

 the centre on the ventral side, from which it narrows almost 

 imperceptibly towards the rounded, sub-capitate ends which 

 are slightly recurved (fig. A). Length, 74 fi to 150 fi. Breadth 

 at centre, 7fi to 9/x; near apices, 5/x to 7)u,. Central nodule 

 homogeneous, very narrow, elongate, slightly arcuate and 



