GASTROPODA. 1045 
Trochonema.] 
propose the specific name expansa. AS we understand it, Bucanospira is a later modification of the type 
represented by Dyeria costata, differing mainly in this, that the aperture is abruptly and greatly expanded 
at intervals as growth proceeds. The old expansions are either all broken away, or, as is more likely, 
reabsorbed. giving a condition precisely asin Z'remanotus. Hach expansion, however, left its mark on 
the interior of the shell as may be seen from the cast of the interior figured above (Fig. 9c). In 
Craspedostoma, Lindstrém, which also has an expanded mouth, the expansion or border differs in being 
thick, cut out on the inner side so as to leave two projecting spurs, and in being developed at one—the 
closing—period only. 
Genus TROCHONEMA, Salter, 
Trochonema and Hunema of SALTER, 1859, Can. Org. Rem., Dec. 1, p. 24. 
? Trochonemopsis, MEEK, 1875, Pal. Ohio, vol. i, p. 219. 
Cyclonema (part.) of HALL, SALTER and others. 
Shell turbinate, umbilicated; spire varying in hight, base generally flattened 
yet sometimes quite ventricose; whoris not numerous (4—8), varying from strongly 
angular to rounded, always with two more or less prominent ridges or angles 
between which lies a broad vertical, usually flat or concave, peripheral space; a third 
ridge usually near the suture, while a fourth generally surrounds the umbilical 
cavity. Other, but smaller ridges may occur though chiefly on the basal half of the 
whorls. Lines of growth crossing the whorls from above obliquely backward, often 
vertical and not infrequently inclined in the opposite way on the peripheral band. 
In the last case the outer lip is broadly notched at the extremity of the upper 
peripheral angle. Aperture usually very oblique; peritreme complete; inner lip 
varying in thickness, not reflected. Type, T. umbilicatum Hall sp. 
This excellent genus exhibits considerable variety in its contents. There is 
scarcely a single character that pertains strictly to all the species, yet, comparing 
one with the other, we find them so closely knit together that to separate them very 
far would mean nothing less than violence to natural classification. We do not 
mean to say that the genus may not be conveniently and yet naturally divided, or 
subdivided, if that is preferable. Hunema, Salter, the type species of which is 
scarcely more than a high and practically imperforate Trochonema, was established at 
the same time as T’rochonema. As at present understood, Hunema is not a well-marked 
genus, while its employment even as a subgenus is attended with difficulties. It 
cannot be maintained on Salter’s characterization, since in shells of this type the 
relative size of the umbilicus isa very unreliable generic character. However, if we 
will select another character of LE. strigillatum, viz.: the very slight obliquity of its 
aperture, the group may have some value. A much better division may be instituted 
for the reception of the group of species typified by our T. pulchellum which eventu- 
ally gave origin to Cyclonema. The separation of this group is certainly convenient 
since it leaves Trochonema (s. s.) as a more compact and sharply defined group. 
Brief definitions of these divisions follow: 
