1906.] NATURAL SCIENCES OF PHILADELPHIA. 137 
While only weakly characterized, this form seems to range over a 
considerable area, and apparently deserves recognition by name. 
B. dealbatus ragsdalei (Pils.). Pl. VI, figs. 16, 17. 
Nautilus, III, p. 122; Man. of Conch., XI, p. 129. 
The shell varies from the ovate shape of typical dealbatus to a more 
lengthened and slender form, and is conspicuously rib-striate, the striz 
white on a tawny or white-blotched ground and weaker on the base of 
the shell. The lip-rib is strongly developed. Three adult specimens 
of the type lot measure: 
Alt. 21.5 18.5 16.5 mm. 
Diam. 10.8 10.3 Sao 
Aperture 10 9.3 Sheree 
Whorls 64 64 6 
Only dead, more or less bleached shells have been taken from the 
top of the Red river bluff at the southern end of Warren’s Bend, 
twenty-five miles northwest of Gainesville, Cooke county, and a mile 
north of St. Jo, Montague county, Texas. 
Across the whole State of Texas nearly 400 miles distant, this form 
reappears on the Rio Grande river, in Val Verde county, in an area 
inhabited also by B. alternatus marie. We are quite unable to find any 
constant differences between these Southwestern shells and the Red 
river types, although the apparent absence of the form in the inter- 
vening territory suggests that the similar forms of the two areas are 
independent parallel modifications of dealbatus stocks, rather than 
actually connected genetically. Yet it is quite possible that the 
widely sundered colonies have been or still are connected through 
the great conchologically unknown area northwest of the oblique line 
across the State marking the limit of our explorations. Dead, bleached 
shells were found in abundance on the high land west of Devil’s 
river, but the living ones for some time eluded us. Finally we found 
them hidden under the dead reversed leaves which thatch the trunks 
of Yuccas, and sometimes under prostrate dead Yuccas—retreats they 
share with the smooth race of Polygyra texasiana (pl. VI, figs. 18 to 
22). The proportions vary a good deal, a series of adult shells 
measuring : 
Alt. 26.5 20 20 21.5 19 16.5 17 mm. 
Diam. 12.5 9.2 10.3 10 10.8 10 eo i 
Aperture 12.5 9 10 10.5) LOL? 9.3 Socks 
Whorls 74 rf 62 64 6 54 64 
