52 THE VOYAGE OF H.M.S. CHALLENGER 



and serving as means of union into zig-zag chains. In acid preparations the differentia- 

 tion of the Synedrce from species belonging to the genus Thalassiothrix is a matter of 

 greater difficulty, but in general this may be done by remembering that the latter are 

 distinguished by lateral rows of much raised thorn-like points so that each of the outer 

 extremities terminates in two projecting apiculi. 



Synedra capitulata, n. sp. (Plate XXV. fig. 13.) 



Lineari-lanceolata, apicibus dilatatis, rotundatis, valvis medio laevibus, ad marginem 

 ordine brevissimarum linearum circumdatis. In mare Philippinarum. 



This very elegant Diatom, which was obtained in a sounding made in the neigh- 

 bourhood of the Philippine Islands, possesses a linear-lanceolate outline. Its extremities 

 are dilated and rounded, and the valve is surrounded by thick short lines, whilst the 

 remainder of the surface is smooth. 



The specific name has reference to the capitate appearance of the extremities. 



Synedra philippinarum, n. sp. (Plate XXV. fig. 15.) 



Gracillima ; valvis angustissime lanceolatis ; apicibus linearibus obtusis ; striis trans- 

 versis continuis. In mari Philippinarum. 



This very slender frustule, also from the sea in the vicinity of the Philippine Islands, 

 presents a slightly arched appearance. The extremities are linear and obtuse, and the 

 strise are transverse and continuous. The fact that this species was represented by many 

 specimens is opposed to the idea that it was originally a freshwater form which had 

 been floated into the ocean, although it may be noted that most slender and crooked forms 

 of the genus are from fresh water. 



Synedra fimbriata, n. sp. (Plate XXV. fig. 14.) 



Ehomboideo-lanceolata ; apicibus rotundatis ; striis transversis, ad marginem evidenti- 

 oribus et vittam linearem constituentibus. Ad oras Philippinarum. 



The valve in this type is sub-rhomboideo-lanceolate. The centre is convex, the 

 convexity lessening towards the rounded extremities. The surface of the valve is orna- 

 mented with continuous transverse strise, which become salient near the margins, and 

 thus form a more prominent outline — a circumstance which has suggested its specific 

 name. 



Synedra lanceolata, n. sp. (Plate XXV. fig. 20.) 



Parva, lanceolata ; apicibus cuneato-acutis ; striis perspicuis transversis, linea lsevi 

 medio interrupts ; striae 1400 in millirnetro numerantur. Ad insulam Heard. 



This frustule was collected near Heard Island in the Antarctic Ocean. It may be 



