80 DUBLIN NATURAL HISTOIIY SOCIETY. 



jectum (Br^b.) it may be known by its lanceolate, not elliptic segments, 

 and its merely apiculate, not spinous extremities. Its lanceolate pointed, 

 not elliptic or reniform, segments separate this species from S. hrevispina 

 (Breb.), while the miicrones of the latter are rather larger, though not 

 more conspicuous. 



Grenus Closteeium (Mtzsch). 

 Closterium directum (sp. nov.) 



Specific Characters : — Prond rather slender; scarcely at all curved, 

 nearly straight, linear, ends truncate ; fillets indistinct ; empty frond, 

 very finely and closely striate. 



Locality: — Several pools, Dublin mountains. 



General Description :— Frond rather slender, about fifteen to twenty 

 times longer than broad, scarcely tapering, lower margin very nearly 

 straight, upper also very nearly straight, but slightly depressed towards 

 the truncate ends, giving the frond a nearly straight outline. Endo- 

 chrome with indistinct fillets, and a conspicuous series of large granules, 

 Empty frond, generally colourless, sometimes faintly reddish near the 

 ends, very finely striate, — the latter character sometimes difficult of de- 

 tection in mounted, but quite evident in fresh specimens. Sporangium 

 unknown. 



Occasionally a distorted specimen is met with, slightly geniculately 

 bent, or a segment sometimes presents a somewhat irregularly curved 

 form; but a similar circumstance is not imfrequently to be noticed in 

 Docidium Ehrenhergliii, which is a straight form. 



Measurements :— Length of frond, Jy to j^; breadth, -^-^-^-^ of an 



Plate II., Eig. 23, frond with endrochrome ; Eig. 24, empty frond ; 

 magnified 200 diams. 



Affinities and Differences :— This species is decidedly the straightest 

 and most linear in form of all the genus Closterium, and it will there- 

 fore be necessary to contrast it with those only whose curvature and 

 tapering are the most slight. 



It may be advisable to contrast this species with C. didymotocum 

 (Corda), G. oUusum (Breb.), C. amllyonema (Ehr.), C. intermedium 

 (Ealfs), C. angustatum (Kiitz.) ; and perhaps C. juncidum (Ralfs), and 

 C. graeile (Breb. ) This species agrees with C. didymotocum in its nearly 

 straight frond and truncate ends, but they difi'er in the following par- 

 ticulars :— in the former, the frond is far more slender than in the latter, 

 which is stout, and in the former the upper and lower margins are pa- 

 rallel, or nearly so ; in the latter, the Iowqy margin is frequently curved 

 upwards at the end, and the upper margin is convex, and in the former the 

 empty fi^ond is far more finely striate than in the latter, while it is more 

 nearly colourless. C. directum is a more slender, more linear, more bacillar 

 form than C. didymotocum, and, so far as comparative outward form merely 

 and length and breadth are concerned, maybe said to bear a relation sliip to 

 that species someAvhat similar to that which Closteriumjuncidum docs to C. 



