472 Dr. Wallich on the Rhizopods. 



Mouth inferior, terminal, oval. Sarcode colourless^ in form, 

 constitution, and arrangement as in Difflugia, Hjalosphenia, 

 &c."— 0;>. cit. p. 145. 



" In composition the shell [of Nebela collaris] is of extraor- 

 dinary character, from the variety in form and arrangement of 

 its elements. Most frequently it is composed of oval or 

 circular disks. The disks usually hold no relationship in size 

 with that of the shell ; . . . . sometimes the shell is almost 

 entirely composed of circular disks, sometimes of oval disks, 

 and frequently the two kinds are intermingled. Sometimes 

 they are of pretty uniform size ; at others, they are intermin- 

 gled, of different sizes. Most frequently the larger disks 

 occupy the fundus and body and the smaller ones the lower 

 part or neck of the shell. Sometimes the larger disks are 

 more or less scattered, with some approach to uniformity, and 

 the intervals are occupied by smaller ones. Indeed, there 

 exists almost any conceivable arrangement of the round and 

 oval disks in the construction of the shell." — Op. cit. p, 147. 

 " Not unfrequently there are found, in association with the 

 usual more characteristic varieties of N, collaris, individuals 

 which have the same form of shell, hut with its structure 

 rather related with that of the ordinary forms of Difflugia. In 

 some specimens the shell is composed of thin and irregu- 

 larly angular silicious plates as represented in fig. 12." — 

 Op', cit. p. 148. 



" Sometimes narrow rectangular plates in different propor- 

 tions are intermingled with the disks, and occasionally the 

 former greatly predominate. Occasionally I have found speci- 

 mens in which quadrate plates, like those of Quadrula sym- 

 metrica,weYe mingled with the more usual structural elements." 

 — Op), cit. p. 153. 



" The specimens vary greatly in the form of the com- 

 ponent silicious plates, which consist of variable proportions 

 of the kind just described, with others which are more regularly 

 rectangular, or in the form of rods, and sometimes with diatoms 

 and round or oval plates, like those which ordinarily com- 

 pose the shell of Nebela collaris. Through such specimens the 

 latter would appear hy transition forms to merge into Difilugia 

 compressa! "—Op. cit, p. 148. 



^ ■ The nature of the singularly varied shell of Nebela col- 

 laris I have not been able to determine with any satisfaction. 

 In the characteristic forms, the elements of structure, the disks 

 and plates, appear to be intrinsic, and not of a foreign character. 

 They appear to be cemented together or conjoined at the 

 borders, and not implanted upon or incorporated with a distinct 

 chitinoid membrane. In breaking the shell the line of frac- 



