GENUS CENTEOPYXIS— CENTEOPYXIS ACULEATA. 183 



pi. XXX, figs. 17-33, pi. XXXI, and figs. 34, 37, pi. XXXII. Commonly, 

 in the same view, the month is more or less sinuous, as represented in most 

 of the remaining figures of Centropyxis in the same plates. The bordering 

 sinuses of the mouth have seemed to me to be variable in number — ranging 1 

 from two to eight. 



When the shell is composed of chitiuoid membrane, and is sufficiently 

 translucent and clear of sand, in the lateral view, as represented in figs. 7, 

 10, pi. XXXI, figs. 29, 31, 32, 36, pi. XXXII, the mouth is seen to com- 

 municate with the cavity of the shell at the upper extremity of the inverted 

 funnel-like base of the latter. 



The borders of the orifice of the mouth appear to be extended in broad 

 bands, corresponding in position with the sinuses of the mouth above indi- 

 cated. From the difficulty of getting and maintaining the shell of Cen- 

 tropyxis in a favorable position for the purpose, I could not satisfactorily 

 determine the exact arrangement of the ascending bands; but they seemed 

 to me to expand at the upper extremity, in some cases to remain free, in 

 others to come into contact with the interior of the roof of the shell. Mostly 

 the upper ends of the bands appeared to be notched. 



At times, in examining specimens, and causing them to roll about in 

 the animalcula-cage, from the mouth beneath, a glimpse could be caught of 

 one or two of the notched ends of the bands, as seen in fig. 5, pi. XXXI. 

 Rarely, a specimen would occur in which a pair of the bands would be 

 distinctly visible, through the mouth from below, as seen in fig. 30, pi. 



XXX, and fig. 35, pi. XXXIII. 



While spineless specimens of Centropyxis, composed of chitinoid mem- 

 brane, approximate Arcella in character, I never could satisfy myself that 

 the shell of the former exhibited the cancellated structure of the latter. In 

 some chitinoid shells of Centropyxis, as those represented in figs. G, 14, pi. 



XXXI, I observed a punctated appearance of some uniformity, but it did 

 not display the clear cancellated arrangement so characteristic of the shell 

 of Arcella. 



Centropyxis seems a decidedly more shy creature than Arcella, and is 

 very much less disposed to put forth its pseudopods. The sarcode is color- 

 less and transparent, and its constituents are usually much less evident 

 than in other ordinary Lobose Protoplasts. Abundant as the animal is, I 

 rarely have had the opportunity of observing it under favorable conditions, 



