490 POLYMORPHISM AND LIFE-HISTORY IN THE DESMIDIACE^, 



Pen. spirostriolatum Barker. (PI.xiii.,f.24). 



Long. 210; lat. 18; ap. 10/x. 



Botany(109). 



A cell with costse more spiral than any I have seen before. 

 The specimen shows very well the development of the membrane. 

 The new growth perfectly hyaline and unstriate, the older portion 

 rufescent and costate. 



Cl. rostratum Ehr. (Pl.xiii., f.25). 



Forma cum endochroma 6-radiata; vesiculis terrainalibus dis- 

 tinctis granulos circ. 7 continentibus. Membrana corporis 

 rufescente, striisnullis. Long.293; long.corp.152; lat. 18; ap.3,4/x. 



Potts Hill(113). 



The beak of the lower semicell approximates to that of Cl. 

 Kiltzingii. This species is a most serious example of the way in 

 wliich obvious and striking characteristics have been ignored 

 liitherto in the diagnosis of the species, and minute differences, 

 which can often with difficulty be recognised, have been elevated 

 into fundamental specific characters. Cl. Kiitzingii, Cl. setaceum, 

 Cl. promim Breb., and elegans Breb., ai'e all merely growth- 

 variations of Cl. rostratum as the nomenclatural type. In this 

 connection it should be noted that W. & G. S. West, in their 

 Monograph, have failed to recognise Cl. pronum Breb. Brebisson 

 in his "Liste," pp.156-157, uses the same words to describe the 

 beak oi Cl. p)'>'onum as of Cl. setaceum, viz.: — " prolongement fili- 

 forme diaphane," the apex "obtus et meme un peu renfle." Cl. 

 pronum, which is not uncommon round Sydney along with Cl. 

 Kiltzingii, has a body about one-half the length of the cell, much 

 longer proportionately than in Cl. setaceiim, and about 8/i broad. 

 Sometimes the body is fusiform and evenly attenuated, but some- 

 times flat on one side (mdre or less) and inflated on the othei'. 

 The latter is Brebisson's form, and gives rise to his remark : — 

 " Ce Closterium ressemble au Cl. gracile." The membrane is 

 generally slightly rufescent and faintly striate, the striae always 

 with difliculty detected. Cl. elegans Breb., in my judgment, is a 



