16 THE NAUTILUS. 



thickened and becomes continuous as shown in figure 11. The ex- 

 ceptional specimen noted above is noticeably larger, but proportion- 

 ately more depressed than the other, measuring 2|xl{x^ mm. But 

 in sculpture it is precisely the same, and I have no doubt that it 

 belongs to the same species. In this, the septum is but partially de- 

 veloped. A very similar specimen in size and appearance, but with- 

 out any appearance of a septum, is noted under group 2. Nearly all 

 of these specimens are " amber-colored," as stated by Smith, but 

 this is caused by a slight ferri-oxide deposit on the surface, which 

 disappears on the application of oxalic acid, and leaves the whole 

 shell of a clear, transparent, corneous color. 



2. Five examples of the primitive stage with no trace of septum. 

 Evidently that growth had not yet begun. Four of them are of the 

 usual size and shape of the " primary " shell. The fifth is somewhat 

 larger and, barring the lack of septum, almost a duplicate of the ab- 

 errant individual noted in group 1. 



3. Three examples in which the secondary growth had been made 

 without forming a septum. In all of them the primary stage is 

 sharply defined by the difference of color, and in color and shape 

 agrees substantially with the usual appearance at that period. In 

 one of them (figs. 3, 6, 9) the posterior slope is not continuous exter- 

 nally, there being a well-marked ''break" between the two stages 

 of growth, and internally the secondary growth flares out at a decided 

 angle all around the posterior margin of the primary shell. 



In the other two examples, the primary shell is rather more con- 

 tracted laterally than usual, but the secondary growth is, on all sides, 

 in a substantially direct continuation of the primary shell. It be- 

 comes more or less irregular, however, as it progresses and the gen- 

 eral effect of the entire shell is that of abnormal growth. None of 

 these shells, however, are referable to any of the described species of 

 Ancylus. Smith states that the Greensport Gundlachia were asso- 

 ciated with Ancylus fuscus and with " more elevated specimens, 

 probably belonging to another species." If his identification of A. 

 fuscus was correct, the difference in the apical sculpture, to say 

 nothing of the general contour of the shell, forbid the union of the 

 two forms. What his other species were, must remain uncertain 

 until his specimens can be examined. Possibly they were non-sep- 

 tate examples of " stimpsoniana," in which the line of demarcation 

 between the primary and secondary growths was not so distinctly in- 

 dicated as in these specimens, which he included with his Gundlachia. 



