19135.} NATURAL SCIENCES OF PHILADELPHIA. 373 
As we searched the range carefully for Oreohelix after finding one 
on the first day, it is probably extinct, not surviving the destruction 
of the woods. There remains a possibility that it may survive in 
some part of the mountains not covered by our collecting stations. 
Thysanophora hornii (Gabb). 
Stations 2, 3, 6, 63, 10, 11, 18, all in the limestone region north 
of Tweed Canyon. 
: UROCOPTID. 
Holospira is rarely if ever found on igneous or metamorphic rock; 
and as the Dragoons are traversed by many dykes, the limestone 
areas where Holospiras live are divided by tracts barren of these 
snails. This has resulted in the differentiation of several species 
which though variable do not intergrade, so far as we know. In the 
Hacheta Range the limestone is continuous, and while there has 
been a good deal of differentiation, the several extreme forms are 
connected by those intermediate in structure and location. 
It must be admitted that our knowledge of the Dragoon Holospiras 
is fragmentary. The whole foothill region, where they abound, 
needs attention. They are easily found, and in large numbers. 
Holospira danielsi n. sp. Pl. XIV, figs. 1 to 3a. 
The shell is cylindric, the upper fourth (or third) tapering to the 
slightly mamillar, obtuse summit. Tilleul-buff, becoming darker 
towards the summit. Nearly 2} embryonic whorls are smooth; 
then slightly retractive axial ribs appear, rather low and delicate 
on the first neanic whorl, after which they become strong, widely 
separated, oblique (retractive) on the conical portion, still more 
widely spaced and vertical on the cylindric portion of the shell, 
where the summits of the ribs are more or less irregular from breakage 
due to being in part hollow there. On the penultimate whorl there 
are 13 ribs (more or less). On the last half of the last whorl the 
ribs become closer (or many may be interposed). The whorls are 
rather strongly convex, the last one tapering downwards, being 
compressed below the periphery; base rimate but not perforated. 
The last fourth of the last whorl is somewhat straightened but not 
built forward beyond the level of the ventral face of the shell. Aper- 
ture rounded-ovate. Peristome narrowly expanded except at the 
upper outer angle, where it is simple and obtuse. The axis is rather 
slender, subequal except at the ends. In the last part of the penult 
and first part of the last whorl there is a strong, short, obtuse colu- 
mellar lamella close to the base; a parietal lamella, much longer 
and usually strong (and frequently a smaller basal lamella). 
