GENUS DIFFLUGIA— DIFPLUGIA SPIEALIS. 125 



variable in the structure of its shell. It is one of the original forms described 

 by Leclerc, in 1815, under the generic name alone. Though not strictly 

 correct to call it spiral, the construction of the shell, especially when viewed 

 by transmitted light, gives rise to such an impression, and thus led Ehren- 

 berg so to name it, and likewise Bailey after him, apparently without 

 knowing that the former had done so. 



In Difflugia spiralis we may recognize one of the enigmatic rhizopods, 

 described, without illustrations, by Schlumberger, in 1845, in the 'Annales 

 des Sciences Naturelles.' I refer to the Lecquereusid jurassica, described as 

 having " a somewhat depressed ovoid-globular retort-shaped shell with a 

 short, wide neck and a terminal circular aperture, from which project 

 thick, cylindrical, blunt pseudopods." 



The shell of Difflugia spiralis is retort-like or flask-shaped, with a 

 usually compressed spheroidal body, and a short, wide, cylindroid neck, 

 which is commonly produced a little more from one side than the other of 

 the shell. The body and neck are, however, quite variable in their exact 

 form and proportions. Commonly the larger specimens with a stony 

 structure accord with the general form indicated. Smaller specimens 

 usually have a proportionately, and often absolutely, longer neck and a 

 more spherical, uncompressed form of body. The neck is mostly straight, 

 but is sometimes slightly bent or curved. Grenerally it is evenly expanded 

 where it joins the body, but is frequently inflated more to one side. The 

 mouth is terminal, circular, or slightly oval, and is neither contracted nor 

 expanded at the border. 



The shell, as ordinarily viewed lying on one of the usually broader 

 surfaces, exhibits a dark line, indicating the presence of an interior partition, 

 which starts from the bottom of the neck on one side and extends in a more 

 or less oblique direction or curve upward toward the opposite side. In 

 some specimens, the partition appears to extend from one half to two thirds 

 way across the shell, and in others nearly or quite completely across in 

 a sigmoid line to the opposite side. The partition apparently continues 

 inwardly the curvature of one side of the body of the shell, and thus gives 

 rise to the impression that the latter makes a spiral turn. 



Ordinarily the structure of the shell so obscures the partition from view 

 that a satisfactory idea of its exact form and relations cannot be obtained. 

 In most instances in smaller and more Iranslucent specimens, in which the 



