KONGL. SV. VET. AKADEMIENS HANDLINGAR. BAND. 22. N:0 8. 65 



The forms of the genus Triploceras are upon the whole very little known, and of 

 those belonging to the gracilis-type from New Zealand which I have seen, there were but 

 few specimens. It is therefore at present difficult for us accurately to group the forms, 

 not knowing what is individual or not. The number of lobes at the ends varies (from 

 2" — 4), as also that of the whorls, although only to a eertain extent. The number of 

 processes in each whorl seems to be relative to the thickness of the cell. The joint neck 

 of the end lobes is sometimes without processes, but sometimes partially niounted as far 

 up as to where the lobes meet. In the latter case an icon may arise similar to the one 

 Maskell has drawn in N. Z. Desm. tab. 12, fig. 23. Possibly the state he has described 

 (1. c. pag. 311) as a new species, tridentatum, may be identical with my subspecies, acu- 

 leatum; but in the latter I have not seen the character, upon which the name of his spe- 

 cies was founded. To judge from his description Maskell appears to have had a compres- 

 sed (or monstrous?) specimen before his eyes. In N. Z. Desm. Add. p. 247 Mr. Maskell 

 has founded a variety, cylindricnm, on specimens cylindrical in section, and having no 

 »rectangular section» • as cc. In Triploceras gracile cc the projections on the lower part of 

 the semicell are almost spreading at right angles, but in *bidentatitm and especially in 

 * aculeatum these as well as the upper ones patent. In the latter form however it some- 

 times happens that they also in the lower part project at right angles. 



Gen. 16. Pleurotaenium Näg. 



1. P. ovatum Nordst. Alg. Brasil. p. 18; Docidium ovatum Nordst. Desm. Brasil. 

 p. 205, tab. 3, hg. 37; Docidium dilatatum Mask. N. Z. Desm. p. 310, tab. 11, 



fig. 11 — -14, non Cleve. 



Crass. 112—126 ,«; long. 320 /u. 



Bay of Islands (91); Kororareka (100); Orakeikorako (299); Paeroa (302). 

 Maskell's statement of the length of its cells, 1 / 33 inch., must be ascribed to a slip 

 of the pen. He must have meant it to be 1 / ee (or 7m) inch. 



2. P. nodosum (Bail.) Lund. Desm. Suec. p. 90; Docidium nodosum Bail. in Ralfs 



Brit, Desm. p. 218, tab. 35, fig. 8. 



Crass. 46—50 fi; er. apic. 24—33 /u; long. 280—360 fi. 



Papakauri (109); Taupo (155); Omatangi (240, 241, 244). 



As it appears to be a distinctive mark of this species (and perhaps of the genus) 

 that the ends of all fully developed cells are crenate, such a state does not seem to give 

 it any claim to rank as a variety. 



3. P. trnncatum (Bréb.) Njeg. Einz. Alg. p. 104; Delpont. Spec. Desm. tab. 19, fig. 7 — 

 11; Closterium truncatum Bréb. apud Menegh. Syn. Desm. p. 235; Docidium tr. 



Rab. Alg. exs. 968. ' 

 Crass. 60 — 65 /u; er. apic. c. 40 fi; long. 600 — ;700 ii. 

 Blueskinbay (40). 



K. Sv. Vet.-Akad. Handl. Btl. 22. N:o 8. 9 



