REPORT ON THE DIATOMACE^E. 163 



Coscinodiscus (?) sp. (?) (Plate X. fig. 10.) 



The form which is represented in this figure is up to the present time unique and must 

 be looked upon as an organism of a very uncertain nature. The valve is oval, and pro- 

 vided with a wide hyaline border. The surface is covered with uniform, densely, but 

 irregularly disposed granules, and the boundary between the hyaline and granulated 

 surfaces is irregidar in form. The specimen figured is the only one which has been 

 observed, and occurs in a preparation made by Dr Rae, and kindly placed by him at my 

 disposal. This being so, the exact systematic position which should be assigned to it must 

 in the meantime remain a matter of doubt, though it may be provisionally assigned to the 

 genus Coscinodiscus. It was collected in the neighbourhood of Zebu, one of the Philip- 

 pine Islands. 



Coscinodiscus diophthalmus, n. sp. (Plate XVI. fig. 4.) 



Valvis cellulosis, duplicem prsebentibus areolam ovalem depressam ; cellulis rotundis 

 grandiusculis ad centrum decrescentibus. In mari Pacifico. 



Among the many interesting preparations made by Dr Pae and forwarded to me 

 by Mr Johu Murray, were some labelled Coscinodiscus excavatus, which could not 

 be reconciled with the Diatom so named by Greville. The latter has been defined 

 in the following manner by Pritchard : 1 — " Disc large, with hexagonal cellules decreas- 

 ing in size towards the centre, which has three conspicuous depressions alternating 

 with the same number of elevations." On the other hand, the valve now in question 

 possesses round cellules, while, in place of the three alternating elevations and depres- 

 sions, there exists two large depressed oval hyaline areas, which appear as perfora- 

 tions, and an equal number of slight elevations. Unless these structures can be 

 compared with the two processes of the genus Auliscus, Ehrenb., they find no analogy 

 among other known Diatoms. The depressions do not certainly show that they 

 are closed by a siliceous plate, since in the interior and at a lower level no other 

 cellulated wall could be discovered, yet the valve cannot be considered as an abnormal 

 or teratological one, because it has been recognised in three collections which were made 

 in widely separated localities in the Pacific Ocean. The true systematic position of this 

 Diatom must accordingly for the present remain a matter of doubt. The specimens 

 observed have been of different dimensions, and the large round cellules ornamenting the 

 valves were observed to decrease slightly in size towards the centre. 



Coscinodiscus diophthalmus, n. sp., var. monojihthalma, nov. (Plate XVI. fig. 7.) 



This variety is provided with a single perforation-like depression and a single elevation. 

 The general sculpturing of the valve resembles that of the preceding species, and, like the 

 latter, the present form was collected in the Pacific Ocean. 



1 Pritchard, op. cit., p. 829 pi. viii. fig. 26 ; Schmidt's Atlas, pL lxv. fig. 1. 



wooc 



