RETORT ON THE DIATOMACE.E. 95 



junction, -which are crowned by denticules. Each is provided with a double furrow near 

 the centre, and the partitions are densely granulated in a quadrate manner. 



This new species has been named from the locality in which it was first observed. 



Melosira glomus, n. sp. (Plate XXI. fig. 10.) 



Frustulis cylindraceo-suborbicularibus, dense quadrato ordine punctulatis, medio zona 

 laevi cinctis. Ad portum Thaiti. 



The spheroidal frustules which compose this Tahitian Diatom present very many 

 granulations save in the smooth linear zone which surrounds each in the middle region. 

 The entire series is irregular on account of the different conditions of development of the 

 component parts, and the valves also vary from the subhemispherical to the depressed 

 convex form. But for the condition of the median band this form would ao-ree with the 

 Melosira labuensis of Cleve ; but its true specific value cannot, in view of the characters 

 quoted, be called in question. 



The specific name has been given from its resemblance to balls of coarse thread. 



Plate XXIII. fig. 4, represents a variety of Melosira glomus from the port of Tahiti ; 

 it may be named Melosira glomus, n. sp., var. major nov. ; while Plate XXI. fig. 11, is a 

 doubtful species of the same genus collected in the Sea of Japan. 



Thalassiosira, Cleve. 



This genus was established by Professor Cleve of Upsala, in his paper On Diatoms 

 from the Arctic Sea, 1 and was characterised by him in the following manner : — " Side 

 view circular, with a row of submarginal spines ; sculpture very minutely cellular, 

 cellules arranged in radiating and curved lines, crossing each other. Front view quad- 

 rangular, with truncate angles, connecting membrane broadly linear, without any distinct 

 sculpture. Frustules, in the living state, connected by means of a central fine thread of 

 mucus into long filaments." 



From specimens of remarkable purity obtained from the Arctic Sea, and more 

 especially from Davis Straits, Cleve established the species Thalassiosira nordenskioldii.' 2 

 This Diatom occurs in these regions in such enormous quantities as to colour the sea for 

 many miles, but I have not observed it in the collections made by the Challenger in the 

 Antarctic Ocean among the South Polar icebergs. It is, however, of the greatest importance 

 to note that I have recently found numerous specimens of Thalassiosira along with many 

 other Diatoms in the alimentary canals of two Echini which were procured at a depth of 

 1340 fathoms in lat. 41° 15' N., long. 65° 45' W. These frustules constituted the food of 



1 Bihang b. Svensb. Vet. Abaci. Hanoi. , Band i., No. 13, p. 6, pi. i. figs, la, 16, \c, Id, Stockholm, 

 1873. 2 Op. at., p. 7. 



