160 Bulletin American Museum of Natural History (Vol. LIII 
Plate X represents a selection of the numerous color forms which 
this species presents in the San Antonio colonies. It is very difficult to 
find two specimens colored exactly alike. 
The ground color is almost always some tint of yellow. The mark- 
ings are usually either black, deep brown, or red. The pattern 
of obliquely axial stripes, as in P]. X, figs. 11 to 14, is one of the most 
frequent. This seems to be an snicatend pattern in the Neritine, appear- 
ing in many otherwise diverse species, especially of the section V2tta. 
Probably it was the original pattern of N. glabrata. 
By weakening of the stripes in zones above and below the middle, 
a banded pattern is formed, as in figures 15 and 18. Further reduction 
of the bands results in a uniform yellow form, as in the series formed by 
figures 18, 17, and 16. 
When the stripes composing the bands become confluent, we have 
such forms as the series figures 20, 25, and 30. 
Splitting and other modifications of the bands are seen in the series 
leading from figures 10 to 6 and 10 to 5. 
When the primitive stripes anastomose, netted and spotted patterns 
result, as in the series figures 14, 19, 24, 29 and 28, characterized by 
increasing predominance of markings over ground color. 
Similar series are formed among the specimens with red markings, 
as indicated by connecting lines on the Plate. 
Rare examples have both red and blackish-brown markings, as In 
figure 35. Figures 1, 2, 3, 39, and 40 are anomalous patterns, relatively 
rare and not readily. connecting with the others. 
The San Antonio colony appears to be a hybrid complex of several 
or many factors. It is contrasted with such colonies as that of Nerztena 
wirginea, figured by M. M. Metcalf,! in which the variation seems to be in 
degree of development of a single pattern. 
The size does not vary much, the usual length being about 7 mm. 
“The smallest of the three species of this group—Neritina (Vitta) 
glabrata—are the most easily gathered, being fairly abundant in their 
favorite places, the sheltered sandy coves with highly brackish water. 
Here, as well as on sand banks, during the slight wash of the waves at 
outgoing tide, they generally form a more or less continuous line of drift 
on the beach. Yellowish tints predominate on their shells, harmonizing 
fairly well with the fine, pale buff sand, but on some the red, brown, and 
565-809, Col PI M.M. 1904. ‘Neritina virginea variety minor.’ American Naturalist, XX XVIII, pp. 
19 
04. oe ae of organic evolution.’ (New York). PIl.1. 
