96 THE VOYAGE OF a M.S. CHALLENGER. 



the animals in question, and so must have been growing in their immediate vicinity at a 

 depth at which, notwithstanding the great distance from the poles, the temperature of the 

 water approaches zero. 



Thalassiosira nordenskioldii, CI eve, var. nov. (Plate XXX. fig. 4.) 



This figure represents a Diatom with a characteristic corona of submarginal spines 

 which was found in the vicinity of the Bermudas ; while fig. 4 bis of the same Plate is a 

 reproduction from the Synopsis des Diatomees de Belgique of Dr van Heurck 1 of the 

 Thalassiosira nordenskioldii of Cleve, the former being magnified 850 diameters, and the 

 latter 600 diameters. In the frustule, now for the first time recorded, the radial striation 

 is so minute that it is difficult to observe even in dried specimens, while the number of 

 prickles or submarginal spines is much greater than in the Arctic form. Hence, although 

 the two might be regarded as distinct species, I prefer to look upon the deep-sea form as 

 a variety of the surface form of Cleve until such time as the former is procured in a living 

 condition, and its history more accurately known. 



Isthmia, Ag. 

 Isthmia enervis, Ehrenb., var. japonica, nov. (Plate XXV. fig. 5.) 



The only form belonging to this genus which has to be recorded is one from the Sea of 

 Japan, which presented an evident analogy to Isthmia enervis, Ehrenb., 2 yet differed from 

 it in several respects. Thus (1.) the profile of the frustule on the zonal side is simply 

 trapezoidal in Ehrenberg's species, while in the Japanese form the two oblique terminal 

 lines are more or less undulating — a distinction upon which much weight cannot be placed. 

 (2.) At the margins of the median band, and adjoining the two sutural lines, a row of 

 larger granules occurs in both cases, as in Biddulphia ; but the band itself is ornamented, 

 in Isthmia enervis, by small round quincuncially-arranged granules, while in the present 

 case the granules are somewhat oval, and are not arranged in a quincunx manner. (3.) It 

 may also be observed that in the Japanese Diatom the strong granules at the two 

 extremities are somewhat different from one another, being on the more obtuse side sub- 

 quadrate and of larger size than on the other side, where they are subrotund. 



Notwithstanding these differences, the frustule from the Sea of Japan must be re- 

 garded as possessing merely a varietal importance, and the distinctive name that has 

 been applied has reference to the locality in which it has been first collected. 



L 1 PL Ixxxiii. fig. 9. 

 2 Ehrenb., Inf., p. 209, pi. xvi. fig, 6 ; Kutz., Bacill., pi. xix. fig. 4 ; Smith, Synop. Brit. Diat, vol. ii. p. 52, 

 pi. xlviii. ; Jan. et Eabenh., Hondur., p. 9, pi. iv. fig. 13 ; Hohenack., Alg. Mar., N. 454 ; Ealfs, Ann., vol. xii. 

 pi. viii. fig. 1. Compare also Isthmia obliquata var. tciiuior, Ag. Conspec, p. 55, and Conferva obliquata, Eng. 

 Bot., tab., 1869.1 



