92 NOVARA DIATOMS. 



Var. (?) nicobaricum. Grun.— Valve broadly lanceolate, some- 

 what obtuse, median line straight, central nodule dilated towards 

 the margin, stride transverse and oblique, transverse stria? distinct, 

 40 to 44 in. "001 The striae become more oblique as they ap- 

 proach the ends. PL 6, fig. 5 a. b. portion of an abnormal 

 valve more enlarged. In Polycystin stone, Nankoori. 



This species has a resemblance to my P. giganteum, but is smaller, 

 shorter, and less obtuse at the apices ; the transverse are somewhat 

 stronger than the oblique striae, which, towards the ends, become 

 somewhat more oblique. 



In one specimen I detected from one to two rows of puncta, en- 

 closed between delicate, often interrupted costae, as I have sketched 

 in fig. 5, b. 



(P. validum is identical with P. rigidum of the Synopsis, and the 

 preceding is only a straight form of the same. I have it from 

 several localities.* The statement that this and many other 

 diatoms have two sets of striae (rows of punctae) is erroneous ; those 

 said to have transverse and oblique striae have them arranged thus : 



if the space between the transverse rows is greater 



'.".*.". than that between the oblique, then the so-called trans- 

 • • • • verse striae are more easily resolved, if, on the con- 

 trary, the space is greater between the oblique rows, then they are 

 more easily detected. The same applies to the so-called transverse 

 and longitudinal striae. In this case, the puncta are arranged in 

 the following manner ' \ \ \ \ * P. K.) 



Xsthmia nervosa. Var. (?) Nankoorensis. Grim. — Frustule 

 somewhat flatter than in /. nervosa; between the costae are one, two 

 (or more) rows of square reticulations, rounded at the angles, which 

 become smaller in size, and greater in number as they approach 

 the margin of the valve. The connecting zone in I. nervosa is con- 

 nected with the valve by a row of large cells. In this form they are 

 w T anting. 



PI. 6, fig. 6, b. portion of valve and connecting zone enlarged 

 to 500 diameters. 



Perhaps a distinct species ; it differs from /. nervosa in the form 

 of the reticulations ; in the latter they are circular or five and six 

 sided. 



Asteromphalus Nankoorensis. Grun. — Broadly ovate or sub- 

 orbicular, centre hyaline, orbicular, slightly excentric ; rays binate, 

 forked, distinct, narrow ; margin divided by two broad rays, reach- 

 ing the circumference : space between the rays about -f- of the 

 valve, a single thin ray not reaching the margin divides this into 

 two unequal parts. The inferior portion of the valve has five 

 narrow short rays, of which the first and fifth are longest. Spaces 

 marked with decussating punctate striae. PL 6, fig. 9. 



Not uncommon on Polycystin stone. Nankoori. 



