208 - DUBLIN NATUBAL HIBTOKT SOCIETY. 



Micrasterias Jenneri (Ralfa) var. 7. 



Granules giving a rather rough appearance to the margin, lateral 

 lobes concave, not bipartite, without eraarginate subdivisions. 



Locality : Bog, near Carrickmore, county of Tyrone. This very inte- 

 resting variety occurred in the gathering kindly forwarded to me by the 

 Hev. R. V. Dixon, and which also contained his new form, Tetrachastrum 

 mucronatum. 



In the monstrosity of Staurastrum dejectum, as shown in the dra-^- 

 ing (Fig. 10), we have both the new segments well developed, and each 

 possessing in the front view its own proper laterally projecting spines; 

 but the interposed segments remain confluent throughout a portion of 

 their terminal margins, forming a bluntly triangular notch at the sides, 

 the whole making but one entire cavity, with the endochrome loosely 

 Scattered within. In the next case, that of Arthrodesmus incus (Fig. 11), 

 the resulting fusion of the new growth, which ought to have formed 

 two new segments, is even greater than in the preceding instance, so that 

 the monstrosity almost represents an individual of three segments, so to 

 speak. Here the interposed new growth has formed, projecting to each 

 side, but one angle, looking as if but one new segment only had been 

 formed, whereas, it must be due really to both segments and spines of 

 the recently- grown portion being confluent. Of this malformation of 

 A. inctts, I have on several occasions seen specimens. 



In the next drawing, showing a remarkable monstrous growth of 

 JSuastrum didelta (Fig. 12), we have a case somewhat similar to the pre- 

 ceding, but presenting additional odd aberrations. The upper and 

 lower portions of the figure represent the side view of the older seg- 

 ments ; between them the new growth has been formed ; but here not 

 only does the direction of the axis of growth assume a course at right 

 angles to the older segments, but, what is curious, the plane of the new 

 growth is at right angles to that of the older. In other words, the new 

 growth, which has formed almost what might be called a new frond, not 

 only has its ends projecting at right angles to the ends of the original 

 one, but it also presents a front view, while the older segments show a 

 side one. The interposed new growth, projecting laterally, has formed 

 the usual linearly notched ends of the species, but one of them has as- 

 sumed a twist obliquely out of the straight direction. The irregulal* 

 space towards the centre of the specimen, as represented in the figure, 

 denotes a portion of the side of the boundary wall, which, upon its inner 

 surface, is there destitute of chlorophyll granules, aff'ording an opportu- 

 nity to look into the central cavity, which thereabouts is more or less 

 empty, but the entire specimen being otherwise, and to all extremities 

 filled with endochrome, in the ordinary manner, as in a normal indivi- 

 dual. 



I exhibit a nearly similar case in Euastrum insigne (Fig. 1 3) ; but 

 the new growth has not assumed a different plane from the old, and it 

 is not so deformed in appearance. Of this monstrosity I have met with two 

 examples. The remaining case is represented by the two drawings which 

 show a state of Tetmemorus Brebtssonii (Figci. 14 & 15), somewhat similar 

 to the preceding condition of Euastrum didelta aJid E. insigne. In one 



