GENUS HYALOSPHBNIA— HYALOSPHENIA PAPILIO. 133 



The shell of H. papilio, pi. XXI, is usually compressed oblong ovoid, 

 but occasionally is compressed pyriform. The compression is about equal 

 to one half the greater diameter. The transverse section, figs. 14, 15, is 

 elliptical, with rounded angular poles. Viewed on the broader surface, 

 figs. 1, 3-5, 7, 11-13, the outline is broadly convex at the fundus, from 

 ■ which the sides slant in a straight or nearly straight line close to the 

 mouth, where they are commonly slightly everted. The lower extremity 

 or line of the mouth is transversely slightly convex. In a comparatively 

 few specimens, in the- view of the broad surface of the shell the outline 

 is decidedly pyriform, as seen in fig. 10. In the view of the narrower side 

 of the shell, the outline is flask-shaped, with the fundus rounded, obtusely 

 angular, or slightly prolonged; and the oral end appears as a concave 

 notch. See figs. 2, 6, 8, 9. 



The mouth is inferior, terminal, and transversely elliptical, with rounded 

 commissures, and is convex in the wider and concave in the narrower direction. 



The shell is buff- or straw-colored, of lighter or darker shade, and rarely 

 nearly colorless. Among thousands of specimens from different localities, 

 I do not recollect meeting with one in which at least a trace of yellow 

 could not be detected. As in other species of the genus, it is perfectly 

 transparent and structureless, nor did I ever find a specimen with adherent 

 extraneous bodies of any kind. The thickness of the shell is pretty uniform, 

 but is slightly greater around the mouth. 



In the view of the broader side of the shell, along the border of the 

 fundus, there may be detected from two to half a dozen minute apertures, 

 around which the shell is slightly thickened. These appear to serve for the 

 ingress and egress of water accompanying the protrusion and retraction of 

 the pseudopods. See figs. 1, 3-5, 7, 10-13. 



The shell of Hyalosphenia papilio exhibits but little variation in size. 

 It ranges from ~^\h. to gj^th of an inch in length by jg^th to ^th of an inch 

 in breadth, and ^th to ith of an inch in thickness. The mouth ranges 

 from ith to ^^ of an inch in breadth. 



me with a small Hartnack microscope, which, from its convenient size and form, I kept on my stndy 

 table. From time to time! was led to make observations on Fresh- water Ehizopods detected in sedi- 

 ments collected vx the vicinity of Philadelphia. A year later, in examinlag water squeezed from sphag- 

 num obtaiaed at Absecom, I observed many individuals of the same singular animal above indicated, 

 but now, understanding its nature, I described it as Difflugia papilio: It was the rediscovery of this beau- 

 tiful form which impelled me tp pursue the investigations which constitute the material of the present 

 work. 



