GENUS DIFFLUGIA— DIFFLUGIA CORONA. 119 



ranged near the mouth, and sometimes form a nearly unbroken row. The 

 denticles of the mouth and the spines of the fundus are likewise made up 

 of sand. Not unfrequently the spines end in a single sharp splinter, or 

 flake, which, in many instances, is of so marked a character that one can- 

 not avoid the impression that it has been specially selected. Mostly the 

 denticles and the tips of the spines are colored ferruginous brown, while the 

 rest of the shell is uncolored. 



As usual in Difflugias, the shell has an uneven surface, varying in this 

 respect mainly according to the proportionate quantity of large and small 

 sand grains entering into its composition. Nevertheless, the grains are 

 united in such a manner that, as before intimated, it is comparatively one 

 of the least uneven in the genus. 



Irregular variations from the usual forms of D. corona are occasionally 

 found. In several instances I have seen specimens somewhat compressed 

 and unsymmetrical, probably from accident. Such a one is represented in 

 fig. 11, pi. XVII. In this, also, the spines were disproportionately large 

 compared with their ordinary condition. Sometimes the spines may be 

 more irregularly disposed, out of the usual proportions, more curved, much 

 reduced in size, and rarely nearly obsolete. I have occasionally met with 

 a specimen in which the mouth was more or less oblique or subterminal, and 

 with a single spine terminating the fundus, as seen in fig. 7. 



This matter brings us to what may be viewed as transitional forms. 

 Fig. 12 represents the mouth of a shell of Difflugia corona, from Lake 

 Hattacawanna, New Jersey. In all respects, the specimen accords with the 

 commoner forms, but has only six denticles to the mouth. It differs only 

 from the large specimen of Difflugia lobostoma, of fig. 8, from Jacksonville, 

 Florida, in the possession of spines to the fundus. As we have seen that 

 the number of the spines in D. corona may be reduced from eleven to one, 

 we may regard the specimen of D. lobostoma, just indicated, as a spineless 

 form of D. corona. Thus, no positive character separates Difflugia corona 

 from Difflugia lobostoma as an independent sjjecies. 



The interior sarcode of D. corona, as visible through its stony wall, 

 appears colorless, with a more or less brownish tinge and darker spots of 

 the same, centrally in the endosarc, dependent on the food. The pseudo- 

 pods present the usual appearance, digitate and palmate, or long and cylin- 

 drical, simple or branching, and ever changing in length and form They 



