26 Conckocelis. 



a shell which contains Conchocelis, it is an easy matter, even with a pocket 

 lens, to see the delicate pink radiating filaments of the Alga. It is not 

 however, till the plant has been freed from the calcareous substance in 

 which it grows that its characters can be made out in a satisfactory way. 

 I have found that the best decalcifying agent is the ' liquide de Perenyi ' 

 the formula for which is given by MM. Bornet and Flahault, which, though 

 it acts slowly, is much more satisfactory in its results than any other 

 solution I have tried. At first the Alga appears in the form of roundish 

 spots, which finally become confluent, their pink colour sharply dis- 

 tinguishing them from the spots formed by any of the other perforating 

 Algae which always, or at least very frequently, accompany them. 



On removing the Alga from the shell by means of the ' liquide de 

 Perenyi/ one at once perceives that these spots are formed of a network 

 of interlaced branching filaments, the central portion of the patch being 

 so closely felted together that it is impossible to make out the ramifi- 

 cations of the filaments ; but at the edges the filaments are not so closely 

 interlaced, and it is easy to trace any particular thread for a considerable 

 portion of its length. 



The thallus is formed of articulated branched filaments, which in the 

 young plants (figs, i and 2) radiate more or less from a central point. 

 Later, by the confluence of several groups, and the consequent interlacing 

 of their filaments, a more or less compact, continuous, horizontal network 

 (fig. 3), which finally covers a considerable portion of the shell, is formed 

 in the superficial layer of the shell. These filaments are of very various 

 widths ; the most slender that I have measured was only 1*5 /x in diameter, 

 while the most robust was 7-5 p, the usual width being about 4^. The 

 cells of which the horizontal filaments are composed are of very various 

 shapes straight or curved, clavate or triangular, or so irregular as to 

 defy description. Below the horizontal layer the filaments swell out here 

 and there into irregularly shaped, septate, simple, or slightly branched 

 inflations ( fig. 5 ), which are, of course, much more robust than the 

 ordinary filaments ; they are often 20-30 /u in diameter, though they 

 seldom reach more than from 70-1 io/* in length. The branching of the 

 ordinary filaments is very irregular ; sometimes for a considerable space 

 a filament is quite simple, and then suddenly, by the outgrowth of 

 lateral shoots, becomes densely branched. The lateral branches are 

 either opposite or alternate, and are either simple or more frequently 

 rebranched, their lateral shoots sometimes anastomosing. The cells of 

 these filaments and those of the inflations are always more or less con- 

 stricted at the joints. 



The inflations (Fig. 5), which usually consist of from two to ten 



