164 THE VOYAGE OF H.M.S. CHALLENGER 



Coscinodiscus rhombicus, n. sp. (Plate XXII. fig. 11.) 



Forma rhomboidalis, apicibus rotundatis ; granulis ad centrum rariusculis nullo certo 

 ordine, ad marginem crebescentibus et sensim in strias radiantes transeuntibus. In mari 

 Japonico. . • 



This elegant valve from the Sea of Japan possesses a rhomboiclal outline. The central 

 space is ornamented by well-defined granules which are free from one another, and 

 arranged in no definite order. They decrease in size, but become more numerous towards 

 the margin, and finally pass into the condition of delicate radiating striae. In its general 

 characters this Diatom recalls the genus Cestodiscus, but the absence of rare distinct and 

 salient granules around the margin prevent it from being ascribed to that genus. The 

 specific name has reference to the form of the outline of the valve. 



Coscinodiscus lanceolatus, n. sp. (Plate XVII. fig. 19.) 



Forma parva, elliptico-lanceolata, granulis vel cellulis stipata a centro radiantibus et 

 decrescentibus. Ad meridiem Australia. 



This elliptico-lanceolate form was procured in the neighbourhood of Sydney, South 

 Australia. It is densely covered with irregular granules or cellules, which decrease in size 

 as they pass from the centre towards the circumference. 



Coscinodiscus ovalis, Roper. (Plate XVII. fig. 18.) 



This form was found in a sounding made near Yedo, in the Sea of Japan. The frustule 

 exactly corresponds to those in a collection of Coscinodiscus ovalis, Roper, 1 which was given 

 to me by the well-known French microscopist Alphonse de Bre'bisson, and it shows marked 

 differences from any of the preceding types. 



Coscinodiscus margaritaceus, n. sp. (Plate XVIII. fig. 3.) 



Mediocris ; valvis margaritarum subeequalium seriebus ab area centrali radiantibus 

 distinctis, quae abrupte ad marginem in punctulorum lineolas transeunt. In mari 

 Antarctico. 



In its general characters this Antarctic valve is closely allied to the genus Cestodiscus. 

 Its form is circular, and it is ornamented by rows of beautiful cellules, which are disposed 

 in radiating lines. The central area is smooth and irregular. Towards the periphery the 

 granules suddenly become small, so that the border is formed by thickly disposed lines of 

 minute points. It differs, however, from the Cestodisci in possessing no prominent 

 points or processes around its circumference, and it must accordingly be looked upon as a 

 specific form of the genus Coscinodiscus. 



1 Micr. Journ., vol. vi. p. 22, pi. iii. fig. 1, 1858 ; Pritchard, op. cit., p. 831, pi. v. fig. 78. 



