82 BRITISH FEESHWATER EHIZOPODA. 



Body discoid, distinguished by the vacuolation of its 

 protoplasm, and the presence, within it, of reniform 

 concretions ; also by its large, block-like, tesselated 

 nucleus, and the peculiar hernia-like pseudopodia, 

 which appear to burst with a sudden action through 

 a toughish cortical layer. Contractile vesicle central. 



Dimensions : About 125 /x in diameter (Ray Lan- 



In ponds near Birmingham, discovered by Mr. 

 Thomas Bolton. 



In his description of Lithamceba (loc. cit., 1879), 

 Professor Lankester says that the pseudopodia differ 

 from those of Amoeba, being rounded and lobular, 

 never digitate, resembling rather "the hernia -like 

 extensions of the protoplasm exhibited in Pelotnyxa" 

 It is easy, he says, to recognize a distinct pellicle, or 

 temporary cuticle, which is formed upon the surface 

 of the protoplasm and bursts when a pseudopodium is 

 formed. In fact it is the rupture of this pellicle which 

 appears to be the approximate cause of the outflow of 

 protoplasm as a pseudopodium. " Probably a still 

 more delicate pellicle forms on the surface of the 

 naked protoplasm, and, in the way just indicated, 

 determines by its rupture the form and the direction 

 of the ' flow ' of protoplasm which is described as the 

 protrusion of a pseudopodium." 



Prof. Lankester discovered an excessively fine reti- 

 culate or vacuolar surface-structure. This differentia- 

 tion of the protoplasm, he says, can be detected all 

 round the margin of the disc-like body, in fact wher- 

 ever the protoplasm is sufficiently free from concre- 

 tions, or food-matter, to allow of proper illumination 

 or inspection. The numerous concretions which may 

 be seen imbedded in the endoplasm are minute, with 

 a tendency towards a reniform outline. These bodies, 

 he thinks, are only a larger form of the refringent 

 granules which are present in great quantity in the 

 protoplasm of the common large Amceba. 



