ARCHER AND DIXON, ON DESMIDIACE.E. 87 



monstrosity almost represents an individual of three seg- 

 ments, 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 malforma- 

 tion of A. incus I have on several occasions seen specimens. 



In the next drawing, showing a remarkable monstrous 

 growth of Euastrum didelta (fig. 12), we have a case some- 

 what similar to the preceding, but presenting additional odd 

 aberrations. The upper and lower portions of the figure 

 represent the side view of the older segments ; 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 assumed a twist obliquely out of the straight direction. 

 The irregular 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 desti- 

 tute of chlorophyll granules, affording an opportunity 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 individual, 



I exhibit a nearly similar case in Euastrum insigne (fig. 13) ; 

 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 Brebissonii (figs. 14 & 15), somewhat similar 

 to the preceding condition of Euastrum didelta and E. 

 insigne. In one the intervening growth has caused the old 

 segments to become somewhat twisted in regard to each 

 other, and, as in the preceding instances in Euastrum, it has 

 assumed a direction at right angles to the axis of the older 

 segments. The last sketch, (fig. 15,) which represents a 

 second instance met with by me of this phenomenon in the 

 same species, shows that the lateral extremity to the right is 

 really what ought to have been normally the new segment on 



