326 FRESHWATER ALG^ OF LISMORE DISTRICT^ 



Monog. ii., p. 171, P1.61, f.26, have just as correctly arranged 

 Cos. Jacobsenii as a variation of Cos. contractum, as the latter is 

 the base of the whole series. It is an instance of the difficulties 

 that attend the arranging of a lot of closely connected, poly- 

 morphic forms, not one of which can be definitely particularised 

 as the direct outgrowth of any other; on a basis, too, partly of 

 outline, and partly of a biological connection which cannot be 

 evaded. 



Cos. OBSOLKTUM var. SiTVENSEf. DENTATA, nom.nov. (Pl.x]ii.,f.3.) 



Long. 54-56, lat. 58-60, isth. 28, crass. 34 fx. 



Lismore (185). 



Cf. Cos. obsoletum var. Sitvense Gutw., in W. & G. S. West, 

 Monog. ii., P1.56, f.4. Neither of Gutwinski's figures, however, 

 (Alg. in Java coll., T.38, f.39, 40) has a tooth at the basal angle, 

 nor is it mentioned in his description, I.e., p. 594. The authors 

 of the Monograph are in error, also, in considering the basal 

 angles to be incrassate, with a central pore. The hyaline tip is 

 formed by an extension of the fine outer primordial membrane 

 of the cell, and the supposed pore is a true conical tooth. Cf. 

 Nordstedt, De Alg. Lugd.-Bat., p. 7, fig.9. In Gutwinski's 

 figures, this outer membrane is shown separated from the cell- 

 wall all round. The sloughing of this membrane is well known 

 in Doc. trabecula. I have observed it also in Cos. glyptodermum 

 W. & G. S. West, in which case the marks of the large depres- 

 sions were plainly visible on it Not only is there a decided 

 tooth at the basal angle in this form, but occasionally from two 

 to four teeth form in a vertical line at the extreme edge, bursting 

 the outer membrane, and giving rise to Cos. auriculatum, which 

 is, therefore, a form of Cos. obsoletum. A mixed form of f. dentata 

 mihi and Cos. auriculatum forma was observed. Cf. PI. xlii., f.5. 

 There is nothing extraordinary either in Cos. obsoletum having a 

 tooth at the basal angle; it is found just as decidedly in Cos. 

 Smolandicum Lund. Gutwinski's description of var. Sitvense^ 

 I.e., p. 594, says "membrana granulata"; this is a mistake, as his 

 own figures show. The membrane is covered with very coarse 

 puncta-scrobiculse. 



