92 THE VOYAGE OF H.M.S. CHALLENGER. 



extremities notably prolonged, and terminated by a well-defined elevation in the form of 

 a process. Around the margin there is a line of sparsely disposed granules or denticules, 

 and the surface of the valve is delicately granulated in a radiating and decussate manner, 

 a few more prominent granules being irregularly disseminated over the same area. The 

 larse central convolute nodule is so arranged as to render the exact determination of its 

 form impracticable. 



The specific name which I have adopted is in honour of my friend, Mr Tulk, who has 

 aided me in many ways with my work. 



Rutilaria edentula, n. sp. (Plate XVIII. fig. 14.) 



Forma grandiuscula. lanceolata ; apicibus longe porrectis, rotundatis in elevatiorem 

 partem terminantibus ; denticulis partem centralem cingentibus, hinc rariusculis, dein 

 deficientibus ; striis egerrime perspicuis, medio radiantibus ; nodulo convoluto distiuctiore. 

 Ad insulas Philippinas. 



This form was found among the Diatoms obtained in a sounding made at Station 211, 

 in a depth of 2225 fathoms. It is much larger than the preceding, and is very different in 

 outline and structural detail. It is lanceolate, but both extremities are much prolonged, 

 and bear at their tips elevations which rise above the plane of the valve. The striation 

 of the latter is extremely delicate in the central part, and can only be determined by the 

 use of oblique light, and the exquisite homogeneous immersion objective of Zeiss. The 

 marginal denticules are thicker than in Rutilaria tulkii, but they become more rare towards 

 the extremities, and finally disappear. The central nodule is less prominent, and appears 

 to be doubled up. 



The specific name which has been applied is intended to recall the absence of marginal 

 denticules at the extremities. 



Melosira, Ag. ( = Gallionella, Ehrenb.) 



This genus was established by Agardh in 1824 for a series of frustules, having cylin- 

 drical, discoid, or globose outlines, and connected into cylindrical Conferva-like filaments, 

 one or two lines passing round each frustule near the centre. Since the frustules are 

 arranged in series, and assume somewhat the appearance of Confervas, it is not surprising 

 that, towards the end of the last century, 0. F. Miiller described, under the name of 

 Conferva armillaris, 1 the Melosira varians of Agardh, 2 the siliceous nature of the walls 

 not being then suspected. 



The union of one frustule with another is either effected by means of convex surfaces or 



1 Nov. Act. Holm., 1873, pi. iii. fig. 67. Rabenhorst places this frustule as a synonym under Aehnanthes 

 longipes, Ag. (Flora Europaea Algarum, p. Ill, 18G4). 



2 Ralfs, Ann. and Mag., pi. ix. fig. 5; Rabenh., Siissw. Diat., pi. ii. fig. 4; Smith, Synop. Brit. Diat., 

 vol. ii. p. 57, pi. Ii. fig. 332. 



