BY G. I. PLAYFAIR. 465 



In this genus all the biological groups and variations of a 

 species are determined by the basal diameter, not by such details 

 as the configuration of the semicell or peculiarities of the apex, 

 which may occur at any stage in the life-history. The clavate 

 c/avaf7im{P\.a]is), the suhc\a,v ate{s^lbclavatum Wittr.), the cylin- 

 drical (»z«a;«m?<m Reinsch, haculoides R. & B.), the excavated 

 haculum, phceodermuin), the undulate, etc., are not, strictly 

 speaking, even variations, let alone species, but merely shapes 

 caused by growth, which may, and to a large extent do, occur in 

 every size of the species from lat.lO to lat.54, and probably also, 

 but of this I have no certain knowledge, right up through the 

 higliest reaches of lat.60-85. 



The chai'acter of the membrane is of no value whatever as a 

 proof of identity. If the scrobiculation or granulation arose as 

 the outcome of forces within the cell, they might -have some 

 weight as distinctive of variation or subspecies; but as a matter 

 of fact, external circumstances, such as continued stagnation, are 

 very largely, if not altogether, responsible for them. In sample 

 No.l09,(N.H.S.), gathered from just a few points along the edge 

 of the swamp at Gardener's Road, Botany, upon a single occasion, 

 there are to be found bacuhim, haculoides, Ehr. f. minor, Ehr. 

 type, Ehr. with 7-undulate base, Ehr. f. elongata, trah. v. crenu- 

 latnm, trah. v. Farquharsonii(Roy), all alike plainly punctate- 

 sci-ohiculate. Any extent of scrobiculation, therefore, may be 

 met with in cells of any age or size. Compare Pl.xi., f.3a, and 

 Pl.xiv., f. 11, where the scrobiculse are replaced by granules ia 

 the same cell. 



Delponte's Doc. Ehrenhergii. — The stout forms of Doc. Ehren- 

 hergii — trah. v. Delpontei mihi, and trah. v. constrictum mihi, are 

 certainly intermediate between the forms of Ehrenhergii proper 

 and trabecula v. crenulatum (the full-grown form of trahecula- 

 itself). They exactly bridge the gap, both in size and character, 

 and might indeed be equally well arranged in the trahecula- 

 roup. However, Delponte(Desni. subalp. p.2'28, T.xx., figs. 1-7) 

 and W. & G. S. VVest(Alg. Madag., p.45, PL v., f.40) have alt 

 accepted them as forms of Ehrenhergii; I have, therefore, included 



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