Mr. C. Meresclikowsky on CuU/ornian Diatoms. 475 



IIG. Nitzschia spathulata, var. hyalina, Greg. San Pedro, 

 not coniinoii. [M.J 



I^ciigtli 043 mm. Endoclirome composed of two plates. 



1 



(IM. V. figs. 18-20.) San 



7. Nitzschia spiralis, s|». n. 

 IVtlro, ratliiT rare. [M.] 



Valve narrow, linear lanceolate, with rounded ends ; girdle- 

 face narrow, linear, slightly attenuated towards the ends ; 

 carinal dots elongated, not accompanied by lines, 9 in 001 mm. 

 Frustule arcuate and twisted near ono of the ends, where the 

 keels cross one another, ])assing from one side of the frustule 

 to the other. Length 0-140-0-175 mm., breadth of the 

 girdle-face 0007-0008 mm. 



This curious form has a very different appearance according 

 to the position of the frustule, as can be seen from the three 

 figures, 18-20, representing the same individual — fig. 18 

 showing it in an almost quite horizontal position, tig. 10 

 when slightly turned around its axis to the left, and fig. 20 

 when still more turned in the same direction. In fig. 19 the 

 U) per end is elevated and the lower turned down; in fig. 20 

 the lower end is horizontal, while the upper one is turned 

 upwards. 



'ihe ttiuclnre of this diatom can be easily 

 understood if we imagine a frustule having 

 the form of Niizscltia signw, in which one end 

 (the inferior) has been twisted to the right 

 side at an angle of about 1^0°: the accom- 

 panying diagram shows how by such a 

 process a fiustule of iV. spiralis would be 

 formed ; ai.d as a consequence of this 

 the lower part of the left keel ab would 

 change its place from the left to the right 

 side of the trustuie (a c), while the other ket 1 

 on the opposite side of the frustule would 

 naturally take the opposite place, thus 

 producing a crossing of both keels. The 

 uj»ptr end is also slightly twisted, but in a 

 much less degree tl.an the lower one. 

 The cndochrome seems to be composed of 

 six granules; but this requires further ex- 

 amination, as the material was not in a very fresh con- 

 dition. 



118. Nitzschiella Lorenziaua (var. incurva?), Grun. San 

 Pedro, rather rare. [S\.] 



33* 



