GASTROPODA. 1015 
Hormotoma gracilis.] 
Typical form. 
PLATE LXX, FIGS, 18-21; ? 22. 
Hight 20 to 33 mm., apical angle very constantly about 18°. Shell small, slender; volutions about 
fourteen in a length of 30 mm. ; rounded, generally with a slight angulation, on which lies the band, a 
little beneath the middle; band seldom preserved, when perfect, rather narrow, smooth, flat or faintly 
concave and margined on each side by a delicate raised line; suture simple, deep; lines of growth fine, 
bending strongly backward from the suture to the band, and beneath this curving very strongly forward 
again, the whole indicating a deeply notched mouth; aperture a little higher than wide, rounded except 
below where it is somewhat produced; inner lip reflected, forming a slightly twisted and thickened 
columella. 
The original of fig. 22, which was found with many specimens like figs. 20 and 21, in the Richmond 
group near Spring Valley, has the whorls too angular. Perhaps it would be better to place it with the 
var. goodhuensis. 
Variety ANGUSTATA Hall. 
PLATE LXX, FIGS. 30-36. 
Has more uniformly rounded whorls and slightly wider band than the typical form. So far as 
observed, this variety never reaches a length of 25 mm., the majority of specimens varying between 
17 and 20 mm. 
Variety SUBLAXA, n. var. 
PLATE LXX, FIGS, 23-25. 
This form is distinguished by its rather loosely coiled yolutions, deep oblique suture, and wide band. 
Variety MULTIVOLVIS, n zar. 
PLATE LXX, FIGS. 26-29. 
Distinguished from the foregoing varieties by its closely wound, vertically depressed volutions. 
? Variety GOODHUENSIS, n. var. 
PLATE LXX, FIGS. 42—43. 
In this form the whorls are unusually high and angular, almost rivalling, in the latter feature, the 
next species, with which, moreover, it was found. But the apical angle is only about 18 degrees, and this 
agrees with H. gracilis, while it is too narrow for H. subangulata. We have only two specimens and there- 
fore do not like to say anything positive about the form. A larger supply of specimens may show it to be 
more distinct than it now appears. At any rate, it seems worthy of recognition as a variety. On plate 
LXX, fig. 22 gives a view of a similar specimen which occurred with H. gracilis and the var. multivolvis in 
the Richmond group at Spring Valley. Possibly this represents a later appearance of var. goodhuensis. 
One or the other variety of H. gracilis occurs in greater or lesser abundance at most localities in the 
the eastern half of the United States and Canada exposing the rocks of the Trenton and Hudson River 
periods. Really satisfactory specimens, however, are rare, especially such as preserve the shell and sur- 
face markings. The var. angustata is scarcely distinguishable in the condition of casts of the interior, in 
which it is usually found, from the typical form of the species, but it is probably safe to say that all the 
specimens of the species found in the Stones River group belong to this variety, since none of the other 
varieties have so far been identified in rocks beneath the Black River group. The variety angustata seems 
to occur as far down as the Calciferous sandstone, since we can see no difference whatever between the 
Stones River form and Murchisonia gracilens of Whitfield. The other varieties are sometimes associated 
with the typical form of the species, but they are readily enough distinguished, either as casts or shells, 
by the peculiarities above mentioned. 
