GASTROPODA. 1033 
Helicotoma planulata.] 
up the development of Helicotoma and conclude that it was derived from Ophileta— 
further, that the Helicotoma line terminated with itself and that Hwomphalus, which 
it resembles in many respects, was not derived from it but directly from Ophileta. 
The connection with Ophileta must determine the position of Helicotoma since 
that genus is most certainly not a member of the Pleurotomariide, while we are 
fully satisfied of its affinities with typical Hwomphalide. 
The Caleiferous formation furnishes at least one unquestionable species of 
Helicotoma, viz.: H. perstriata Billings. There is a small species (Jess than one-half 
an inch in diameter) in the Shakopee of Minnesota, that seems to differ very little 
except in size from our H. umbilicata of the Stones River group. Other species of 
the Stones River group are H. tennesseensis Safford, H. declivis Safford, H. planulata 
var. robusta U. and S., H. planulatoides Ulr., H. verticalis Ulr., and H. granosa Ulr. The 
Black River group has H. planulata Salter, the type of the genus, and H. muricata, 
H. spinosa and H. larvata of the same author. From the Quebec group of Canada 
Billings described five species (ewcharis, gorgonia, misera, proserpina and tritonia) with 
characters apparently in strict accordance with Helicotoma. Only H. marginata Ul. 
is known to us from strata of the Cincinnati period. H.maresi Etheridge, an Upper 
Silurian shell, and the Devonian H. serotina of Nicholson, probably belong to some 
other genus. 
HELIcoTOMA PLANULATA Salter, and var. ROBUSTA, 7. var. 
PLATE LXXIV, FIGS. 15—17. 
Helicotoma planulata SALTER, 1859, Can. Org. Rem., Decade I, p. 14. 
H. planulata is distinguished from nearly all other species of the genus by having from three to six 
strong, simple or double, revolving lines on the outer side of the whorls. Beneath the marginal notch- 
ridge the outer side is more or less distinctly concave. The summit of the ridge may be on the same plane 
in all the whorls, but, as a rule, on each it is a little lower than on the preceding turn. Within the ridge, 
which is sharply elevated and marked on its outer side by an impressed line, the depressed upper side of 
the whorls is quite flat. The under side of the whorls may be regularly convex or an obscure angle may 
form the boundary of the umbilicus. A full grown individual has five whorls. On plate LXXIYV, figs. 
16 and 17, are two views of what we consider as a typical example of the species. 
Var. ROBUSTA, n. var. 
PLATE LXXIV, FIG, 15. 
This variety is founded on a single imperfect specimen. It has revolving lines like H. planulata, 
but differs in certain respects too obviously to be referred to that species without question. In the first 
place its whorls enlarge more rapidly both in hight and width. The inner whorls are missing, but we are 
well satisfied that the specimen consisted originally of no more than four whorls. Next the concavity of 
the upper part of the outer side of the whorls is scarcely noticeable. Finally the lines of growth cross 
this side more obliquely. 
Formation and locality.—The typical form of this species, excepting a single example from an unde- 
termined Trenton horizon in Lincoln county, Missouri, is only known from the Black River limestone at 
Pauquettes rapids of the Ottawa river, in Canada. The type of our var. robusta is from the Stones River 
group in Jo Daviess county, Illinois. 
Collection.—K. O. Ulrich. 
