REPORT ON THE DIATOMACE.-E. 91 



Owing to the great rarity of the Rutilarise, the present forms have not been observed 

 from the zonal aspects; and, with the exception of Rutilaria epsilon, Grev. 1 — whose 

 convolute nodule recalls the shape of the Greek letter from which its specific name has 

 been derived — it has been found impossible to determine the form of the nodule. 



Hitherto no living specimens belonging to this very interesting genus have been 

 recorded, and it is therefore of the highest importance that such specimens should have 

 been procured during the Challenger Expedition. It is true, indeed, that Professor Cleve, 

 of Upsala, records in his Memoir f on some New and Little Known Diatoms, Plate iv. 

 fig. 57, a, b, under the name of Rutilaria recens, Cleve, two curious lanceolate forms 

 which were brought home by the "Eugenie" Expedition 3 from the Galapagos Islands. 

 These, however, have not the slightest trace of the convolute central nodule — a circum- 

 stance which should serve to exclude the organisms in question from the genus to which 

 they have been ascribed by him — unless, perchance, it can be proved that one of the 

 valves is normally devoid of such a nodule, as happens in Cocconeis. But this peculiarity 

 has not hitherto been substantiated, and it seems an improbable one in the case of a genus 

 whose frustules are disposed in series. 



Of the specimens collected by the Challenger, one was obtained in a surface gathering, 

 and so must have been in a condition of active vitality. 



Rutilaria tulkii, n. sp. (Plate XVIII. fig. 11.) 



Valvis elliptico-lanceolatis, apicibus productis, rotundatis et in 'partem elevatiorem 

 exeuntibus ; denticulis rariusculis marginalibus circumductis, et aliis medio irregulariter 

 distributis ; striis tenuissimis medio radiantibus, ceterum decussatis, nodulo centrali con- 

 volute Ad Samboangan ex insulis Philippinis. 



This organism was found in a surface collection, in which hardly anything but small 

 animals occurred. After washing these with distilled water, a preparation composed 

 chiefly of spicula wa3 obtained, but a more minute examination revealed the presence 

 of the two small elegant frustules here figured, which were similar to one another, and 

 arranged in a cruciform manner. I at first believed that this peculiar arrangement corre- 

 sponded to the intersection of the axes of the figures, as occurs in some other genera, such 

 as Camjiylodiscus, but after submitting this view to my friend, Mr Tulk, I became con- 

 vinced that the frustules are enabled to have this disposition because of the peculiar form 

 of the central nodules which form the real points of union between them. 



A similar arrangement was also observed by Dr Gray, who had artificially caused two 

 Kutilarian frustules to move from their normal parallel position. 



Rutilaria tulkii possesses a small but elegant elliptico-lanceolate form, having its two 



1 Quart. Journ. Micr. Sci., n. s., vol. iii. p. 228, pi. ix. fig. 1. 



2 Kongl. Svenska Vetensh.-Akad. Handl, Band xviii. No. 5, Stockholm, 1881. 



3 The Expedition of the Royal Swedish Frigate "Eugenie" took place during the years 1851-53. 



