REPORT ON THE DIATOMACE/E. 165 



Coscinodiscus radiatus, Ehrenb., var. abyssalis, nov. (Plate XXIX. figs. 2, 11, and 15.) 



Those figures represent a Coscinodiscus which was found in the interior of two 

 Echini procured from a depth of 1340 fathoms at Station 47, lat. 41° 14' N., long. 

 65° 45' W. The differences observable between the frustules tend, however, to lead one 

 to believe that one has to deal with forms having no relation to one another. The 

 drawings have been made from the appearance presented by one valve mounted in a 

 dry air cell instead of Canada balsam, and in such circumstances when examined under 

 the most perfect homogeneous immersion objectives, constructed by Zeiss of Jena, or 

 by Eeichert of Vienna, and others, a different image is obtained at each slightest 

 focal change, so that it is not easy to determine which should be regarded as typical. 

 These different appearances, however — apart from those caused by diffraction — reveal the 

 minute details of the ornamentation of the organism. Thus, although I regard the very 

 small granules which limit the hexagonal areolae in fig. 2 to be a real structural peculiarity, 

 they cannot be observed in Canada balsam preparations. In the latter preparations the 

 surface is found to be covered with areolae, which radiate from the centre to the peri- 

 phery, where they gradually diminish in size, so that it presents affinities to Coscinodiscus 

 radiatus, Ehrenb. 1 On comparing it, however, with the specimen of that species given 

 in the Typenplatten of Moller, the areolae are found to differ in size in the two cases, 

 being in the new form about one-third larger. Thus it must be regarded as a variety of 

 Ehrenberg's species, its varietal name having reference to the fact that it was procured in 

 deep water in the Atlantic. It is desirable that the two forms should be accurately com- 

 pared when both mounted in the dry state. 



Willemoesia, n. gen. 



Several of the curious and interesting forms shown on Plate VIII. figs. 8, 8 a, and 

 8 b, have been observed from different localities. The three frustules represented are all 

 elongated, and are closely related to one another. All are granulated, but in the first 

 the granules are disposed in an indefinite manner, while in the second and third the 

 punctations are uniformly distributed over the valves, being in the second decussate, 

 but in the third irregular. The form of the first is long and cuneate, while that of the 

 others is sublinear, but in all three one extremity is cuueately, while the other is simply, 

 rounded. 



The fact that several specimens of these forms have been observed from different 

 localities is opposed to the belief that they are teratological or anomalous forms, and as 

 they all present some common characteristics, while each retains its own special and 

 distinctive marks, they may well be regarded as three types of a new genus. 



1 Ehrenberg, Mikrogeologie, pi. xxL fig. 1 ; Smith, Synop. Brit. Diat., pi. iii. fig. 37 ; Pritchard, op. ciL, 

 p. 830, pi. xi. figs. 39 and 40. 



