REPORT ON THE DIATOMACEiE. 53 



distinguished from a Navicula by the absence of the characteristic nodule of the latter, 

 but its stria3 are interrupted by a simple longitudinal line. 1 This feature, taken in con- 

 junction with the cuneato-acute appearance of its extremities, constitutes a very distinct 

 specific type. 



Synedra lanceolata, n. sp., var. thaitiensis, nov. (Plate XXV. fig. 18.) 



This frustule, which is similar to the preceding, was found in a gathering from the port 

 of Tahiti. It may, however, be distinguished from Synedra lanceolata by its somewhat 

 finer stria?, which are interrupted by a fine line, but it cannot be regarded as more than 

 a variety of that type. 



Synedra atlantica, n. sp. (Plate XXV. fig. 16.) 



Lanceolata, elongata ; apicibus rotundatis ; striis evidentioribus transversis continuis, 

 binis lineis submaroinalibus unilateraliter sectis. In Oceano Atlantico meridionali. 



This Diatom was obtained from a soundino; made in the middle of the South Atlantic. 

 Its valves are lanceolate, and are provided with rounded apices. The striation is well 

 marked transversely directed and continuous, but is cut on one side by two submarginal 

 lines, the signification of which is not manifest, although they must be regarded as 

 characteristic of the species. 



Thalassiothrix (Grun.), Cstr. 



Among the surface collections made in the Bay of Yedo and in the waters around 

 Hons-Kongr there has been found in great abundance a Diatom of a bacillar form, which 

 is either long and straight, or short and slightly curved in appearance, and which 

 generally occurs in small groups, the frustules being arranged either in a radiating 

 manner or forming a zig-zag series. The individual Diatoms are bordered by lines of very 

 elevated granules, so that the outer extremities are crowned by two apiculi. Similar frus- 

 tules have also been observed by me in surface collections made in the Adriatic off the 

 coast of Dalmatia, and on the Italian coast at Rimini and Fano. In specimens procured at 

 the last-named localities, and which had not been subjected to any incinerating process, the 

 frustules were found in groups of not more than eight, and were simple or double and 

 united in a radiating manner, the inferior extremities being sunk in a small transparent 

 cushion of the form of an armilla, which is destroyed by the action of heat. Not un- 

 frequently a few similar frustules were seen in zig-zag position, and it was of interest to 

 observe that when a normal radiating group of simple frustules was undergoing fission, 

 and so becoming double, the cushion broke by the separation of two contiguous frustules. 



1 The double central line has been figured by mistake. ' 



