E. PENARD ON SOME RHIZOPODS FROM SIERRA LEONE. 303- 



Lesquereusia mimetica sp. nov. (PI. 10, Fig. 7). 



This very remarkable Rhizopod, whose structure presents some- 

 thing unwonted and strange, is at the same time one of the 

 largest, attaining on an average about 400 fx in length ; but, 

 curiously enough, and just like what we saw when treating of 

 Pontignlasia compi^essa, two series were found, one embracing 

 specimens varying from 370 to 420 fx in length, the other much 

 smaller, about 310 /x. Some transitional cases, however, were 

 found, but they were very few.* 



The test (Fig. 7), built of siliceous sand particles imbedded in 

 a chitinoid material, looks at first sight like an ovoid, slightly 

 compressed, DiflHugia shell, about one and a half times as long 

 as broad, rounded behind and tapering anteriorly into a terminal, 

 circular mouth. 



But a more thorough examination proves the structure to be 

 quite different. From below one of the corners of the terminal 

 orifice a dark line is seen, going down towards the posterior part 

 of the shell, cutting, in appearance, the test in a direction parallel 

 to the side opposed to the starting-point of that line, and ter- 

 minating abruptly somewhat behind the middle of the shell. 



This line represents, in fact, an inside partition, yellowish, 

 chitinous, yet mixed with very small siliceous particles ; and this 

 partition is double (at least must be originally), an inner sheet 

 representing the body envelope, an outer one the ventral wall 

 of the tube characteristic of the genus Lesquereusia. 



The long tube, in fact, has been pressed against the shell, 

 soldered to it ; everything, at the same time, has been smoothed 



* This existence of two parallel series in a given locality, if exceptional, 

 is not very rare among Rhizopods. Without pretending to give any serious 

 explanation of the fact, I surmise that in such cases one has to do with 

 two " generations."' The testaceous Rhizopods divide, perhaps several 

 times in a season, the plasma building a new shell where part of the 

 contents of the old are introduced, and, when conditions are favourable,, 

 that new shell is a trifle larger than the old. After five or six divisions, 

 the last-formed tests are much bigger Lhan the fir^t original ones ; and 

 a time comes when nearly all specimens in a given station have attained 

 what might be called an optimum, which cannot be exceeded in that 

 station. But it might happen that in the very same locality, " little ones " 

 have been produced in the meantime (from spores (?) or cysts (?) ), and 

 these, having not yet attained the optimum, can be sharply distinguished 

 from the old generation. 



