416 PROCEEDINGS OF THE ACADEMY OF [April, 
tions in outline show what may occur in a single intergenerant colony. 
The specimens from locality 806 show even greater differences, of 
which the following are the extremes: 
Alt. 34 Diam. 34 mm. 
ol 33 
19 37 
19.5 39 
I should like to suggest the name discoides, merely as a convenient 
term by which to know the variation represented by the last two shells 
(Pl. XXXVI, fig. 4). I must say, however, that this suggestion 
would be unfortunate if it resulted in the division of the series ob- 
tained from locality 814. It seems to me, rather, that some physio- 
logical peculiarity has destroyed the diagnostic value of the elevation 
of the spire. The upper whorls differ less than the lower, and in the 
most elevated forms the suture of the later whorls is much below the 
keel of the preceding whorl, as if the slant of the spiral had been 
abnormally diverted downward. 
Pecilozonites nelsoni var. callosus n. var. Pl. XXXVI, fig. 5. 
Shell smaller than the typical form, shiny, with heavy ribbed striz, 
colored with a broad yellowish-brown peripheral band on a white 
ground. Whorls a trifle more than nine, increasing regularly and very 
gradually. The suture does not change its character nor become de- 
flected from the peripheral line of the preceding whorl. The usual 
peripheral angle is almost obsolete. The base has a stronger angle 
about the umbilical perforation than is usual in the species. The 
peristome is greatly thickened on the inside from 1 mm. at the suture 
to fully 2 mm. near the columella. A prominent callosity covers the 
parietal wall of the aperture. 
Alt. 24, diam. 33 mm. 
The combination of small size and large number of whorls is charac- 
teristic. The ratio of height to diameter is more constant than in 
the typical form, and the tendency to produce the callosity is very 
marked. 
Type from locality 818, others from 818 and 807. 
The stability of the variety, occurring as it does in the oldest and 
the latest formations, is the most interesting thing about it. It is also 
my excuse for regarding such slight distinctions in a remarkably vari- 
able species. 
I suppose the color patterns of Pecilozonites nelsoni were essentially 
the same as those on the living Pecilozonites bermudensis. For ex- 
ample, the type specimen of callosus probably had a dark brown band 
