EEPOET ON THE DIATOMACEiE. 39 



This form is remarkable on account of its small size and the large granulations that 

 occur on its surface. In profile it is slightly sigmoid, the raphe beiug much more so, so 

 that the extremities are unequally divided by the raphe. The longitudinal axis is almost 

 four times as long as the transverse axis. 



This type is not uncommon in the Sea of Japan, and its specific name has reference to 

 this circumstance. 



Toxonidea, Donkin. 



Under this head are comprised a few navicular forms -which, whilst they present a 

 granulation identical with that of Pleurosigma, have the extremities of their valves more 

 or less curved in the same direction, the middle line being, at the same time, decidedly 

 arcuate. 



Toxonidea challengeriensis, n. sp. (Plate XXVI. fig. 15.) 



Forma gracillima lanceolata ; apicibus elliptice inflatis et symmetrice curvatis ; raphe 

 medio subcentrali ad apices excentrico ; striis densissime decussatis. Ad portum Thaiti. 



Amongst the many interesting types which were obtained from the washings of sand 

 brought from the port of Tahiti, and from no great depth, the singular navicular form 

 now being considered was observed. It possesses a very long and slender lanceolate form, 

 having the two extremities strongly bent in the same direction. The raphe remains almost 

 central throughout the greater part of the valve, but becomes eccentric near the more 

 attenuated extremities. 



Toxonidea challengeriensis, n. sp., var. nov. (Plate XXVI. fig. 14.) 



We have here represented a small but interesting form first observed by Cavaliere 

 Alessandro Garbi of Florence, among some algaa from the Mediterranean. Although 

 differing sensibly in size, no distinction between the striation of the Tahitian and Mediter- 

 ranean specimens was observed, so that the latter has been regarded as a variety of 

 the former. It was first recorded by Garbi in the Tirreno Sea. 



Amphiprora, Ehrenb., Kg. 



Of all the genera of Diatoms that of Amphiprora is one of the most difficult to under- 

 stand. Pritchard defines it as follows : — " Frustules free, simple in front view, constricted 

 at the middle ; valves convex, with a longitudinal wing, and central and terminal nodules ; 

 strise, when present, transverse." I am of opinion that the frustule is naviculoid, and 

 that on the axis, and as an emanation from the axis or from the raphe, bilobate wings 

 appear. 



