416 PROCEEDINGS OF THE ACADEMY OF [April, 



tions in outline show what may occur in a single intergenerant colony. 

 The specimens from locahty 806 show even greater differences, of 

 which the following are the extremes: 



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 

 (PI. 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 

 al^normally diverted downward. 

 Poecilozonites nelsoni var. callosus n. var. PI. XXXVI, fig. 5. 



Shell smaller than the typical form, shiny, with heavy ribbed stria), 

 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 

 ])eripheral 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 numl^er 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 docs 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 reniarkal^ly \'ari- 

 able species. 



I suppose the color patterns of Poecilozonites nelsoni were essentially 

 the same as those on the living Poecilozonites bermudensis. For ex- 

 ample, the type specimen of collosus jirobalily had a dark lirown band 



