274 Mr. J. llalfs on the Diatomacese. 



they seem a part of the front of the frustulej the central portion 

 appearmg lilcc a band between them. The mode of growth in 

 this genus is also similar^ but it differs in having all the angles 

 elongated and equal. 



The filaments are attached by one of the angles of the basal 

 frustule. At fii'st the frustidcs are connected mth each other at 

 both the adjoining angles, and as these angles are elongated, a 

 small vacant space is inclosed between the connecting processes 

 of the frustules. Ultimately, and after a partial separation has 

 taken place, they cohere only by the alternate angles and form a 

 zigzag chain. 



1. B. pulchella, Gray. Frustules distinctly reticulated; lateral sur- 

 faces with one or three rounded projections between the angles, 

 and marked with a few distant striae, which appear to arise from 

 the depressions between the projections. Gray, Nat. Arr. of Br. 

 Plants, vol. i. p. 294 : Kutz. Syn. Diatom, p. 610. Diutoma Bid- 

 dulphianum, A^. Consp. Diatom, p. 54; Harv. Br. Alg. p. 201. 

 Conferva Biddulphiana, Eng. Bot. 1. 1762 ! (upper figures)*. 

 Southampton, Miss Hill; Ilfracombe. 



It is brownish when recent and becomes paler in diying. 



Filaments elongated, attached ; frustules generally broader than 

 long, but varying much in figm'C as the central portion, which is 

 at fii'st very narrow, gradually increases in size until it becomes 

 broader than long. The lateral portions have at least one, and 

 sometimes in the larger specimens three roimded projections, be- 

 tween the angles. None of these project so much as the angles, 

 and the central one is larger than the others, which are often 

 nearly flat. From the intervals between the projections, striae 

 proceed to the line which separates the central portion from the 

 lateral one ; generally these strife are single, but sometimes two 

 proceed from the same point and diverge from each other as they 

 approach the central portion. The strise are often united by ir- 

 regular anastomosing lines ; there is frequently also a line sm-- 

 rounding the base of the projecting angles. Between the strise 

 the lateral portions are cellulose, exactly like the central. 



This cellulose structm-e is easily observed under a moderate 

 power of the microscope. The angles are romided, and occasion- 

 ally constricted at their base, but more frequently not so. There 

 is no constriction at the junction of the lateral portions with the 

 central one. 



This species is a most beautiful microscopic object. 



Plate VIII. fig. 3. Biddulphia pulchella. 



2. B. aurita. Frustules very minute ; cellulose structure indistinct; 

 lateral portions without strise. Diatoma auritum, Lyngb. ; Ag. Syst. 



* The lower figures seem to have been drawn from Dialoma teniceforme. 



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