4^0 



MR JOHN RATTRAY ON A 



surface, those adjoining it radiating on both sides. At the narrowest part of 

 the constriction, between the distal and median inflations, another single stria 

 on each side of the median raphe stands at right angles to the median longi- 

 tudinal axis of the frustule. On both sides of the central stria of the median 

 inflation the stria? are again disposed in a radiating manner, as indicated by W. 

 Smith, Van Heukck, &c, but this radiating condition does not in all cases 

 extend to the proximal extremity without interruption, the striation of the 

 proximal inflation repeating exactly, though in miniature, the arrangement 

 found in the median. (4) The strise extend from the outer margins well up to 

 the central raphe, which is by no means so pronounced in size as is indicated 

 by any of the figures given by Van Heukck. The strise on the valves are often 

 somewhat indistinct. (5) The terminal proximal un ornamented areola is very 

 minute, not exceeding 0*0012 mm. in diameter in the direction of the longi- 

 tudinal axis. 



Table giving the Lengths and Breadths of Entire Frustides, and of parts of the same, with the 

 average number of Stria; in each case. All the Measurements are given in Millimetres : — 



No. 



Length of 



entire 

 frustule. 



Length of 



distal 

 inflation. 



Length of 

 median 

 inflation. 



Length of 

 proximal 

 inflation. 



Breadth of 



distal 

 inflation. 



Breadth of 

 median 

 inflation. 



Breadth of 

 proximal 

 inflation. 



Breadth of 



distal 

 constriction. 



Breadth of 



proximal 



constriction. 



Strife in 

 01 mm. 



1 



0-0650 



0-0150 



0-0275 



0-0200 



0-0125 



0-0112 



0-0068 



0-0075 



0-0050 



10 



2 



0-0575 



0-0112 



0-0250 



0-0188 



0-0125 



o-oioo 



0-0068 



0-0075 



0-0050 



10 



3 



0-0725 



0-0175 



0-0300 



0-0225 



0-0150 



0-0125 



0-0075 



o-oioo 



0-0068 



10 



4 



0-0600 



0-0125 



0-0262 



0-0188 



0-0125 



0-0125 



0-0062 



0-0075 



0-0055 



10 



5 



0-0850 



0-0162 



0-0400 



0-0263 



0-0137 



0-0125 



0-0062 



0-0075 



0-0050 



8-5 



6 



0-0675 



0-0137 



0-0300 



0-0213 



0-0125 



0-0106 



0-0055 



0-0056 



0-0050 



10 



7 



0-0625 



0-0137 



0-0275 



0-0188 



0-0125 



0-01 18 



0-0056 



0-0062 



0-0050 



10 



8 



0-0625 



0-0125 



0-0275 



0-0200 



0-0125 



o-oioo 



0-0056 



0-0062 



0-0050 



10 



9* 



0-0750 



0-0162 



0-0325 



0-0238 



0-0137 



o-oioo 



0-0062 



0-0068 



0-0050 



8 



10* 



0-0725 



0-0150 



0-0325 



0-0225 



0-0131 



0-0112 



0-0062 



0-0062 



0-0050 



8 



11 



0-0650 



0-0125 



0-0275 



0-0225 



0-0125 



0-0105 



0-0055 



0-0062 



0-0050 



10 



12 



0-0700 



0-0150 



0-0300 



0-0225 



0-0125 



o-ono 



0-0055 



0-0062 



0-0048 



10 



13 



0-0575 



0-0125 



0-0250 



0-0175 



0-0112 



o-oioo 



0-0055 



0-0056 



0-0050 



10 



14 



0-0650 



00150 



0-0275 



0-0200 



0-0125 



0-0125 



0-0056 



0-0075 



0-0050 



10 



16 



0-0650 



0-0125 



0-0275 



0-0225 



0-0125 



0-0112 



0-0056 



0-0070 



0-0050 



<) 

 9 



Average 

 Approx. 



| 0-0658 



0-0138 



0-0285 



0-0209 



0-0127 



0-0112 



0-0059 



0-0069 



0-0051 



The length of the apical crest in all cases was = 0*0025 mm., and this added 

 to the lengths of the three inflations, each reckoned from the narrowest part of 

 the constrictions, makes up the entire length of the frustule. 



In taking the averages, Nos. 9 and 10, which are varietal forms, have not been taken into account. 



