•136 MR JOHN RATTRAY ON A 



frustules shows a very slight subcentral inflation on the concave margin. 

 Length, 01000 mm.; breadth, 00125 mm.; striae, 8 in 0*01 mm. Specimens of 

 smaller size not unfrequent. 



35. Eunotia major (W. Sm.), Raben., var. semelconstricta, nov. (PI. XXIX. 



fig. 8.) 



Rare. This curious form is closely akin in general outline to the Eunotia 

 pectinalis, var. biconstricta of Grunow (Van Heurck, op. cit., pi. xxxiii. 

 fig. 19). It agrees essentially with the typical form of Eunotia major in its 

 striation. The great ventral constriction is somewhat nearer one extremity of 

 the frustule than the other, and its two sides are quite unsymmetrical, that 

 next the extremity towards which it is placed being considerably more convex 

 than the opposite side. There is sometimes a second slight constriction on the 

 concave side, where the inflation bounding the greater constriction passes into 

 the all but straight " ventral " line, which proceeds from it to the extremity. 



Length, 0*1050 mm. ; greatest breadth, 00125 mm. ; breadth at great con- 

 striction, 00100 mm. Striae, 9 in 001 mm. 



The drawing in the plate represents a form in which the constriction was 

 only of moderate depth. In some specimens observed it is at once more 

 marked and bounded by more convex margins. 



36. Eunotia pectinalis (Kiitz.), Raben., var. undulata, Ralfs. 

 = Himantidium undulatum, W. Sm. 



The undulations on the convex side are five in number, and of these the 

 median is often much more pronounced than in the form figured by Van 

 Heurck (op. cit, pi. xxxiii. fig. 17). Moreover, the inflation on the concave 

 side is often much more sharp, whilst the transverse striation is relatively 

 more dense in the areas intervening between the central portion and the 

 terminal parts. Specimens also occur in which the dorsal undulations are not 

 more than three in number, and of these the central is the more pronounced. 

 In such forms there is the same median " ventral " inflation opposite the median 

 dorsal as in others with the usual five undulations. 



Length of specimen, 0-0650 mm.; breadth at central inflation, 00075 mm.; 

 breadth at narrower parts adjoining the centre, 0050 mm. Not very 

 abundant. 



37. Eunotia gracilis (Ehrenb.), Raben., nee. W. Sm. 

 = Himantidium gracile, Ehrenb. 

 Not unfrequent. The specimens agree essentially with that figured by 

 Van Heurck (op. cit., pi. xxxiii. figs. 1, 2), the valves being regularly lunate, 



