GASTROPODA. 1029 
Ophiletina. ] 
the upper side of the whorls, the band, in low-spired pleurotomarians, being almost 
invariably situated on the periphery. Again, the rounded character of the whorls 
of the interior casts, which necessitated a strong deposit of shell beneath the 
external keels, the lower especially, recalls a common condition among species of 
Ophileta, Euomphalus and Pleuronotus, but not of any of the Pleurotomariide. 
According to our view, Hisingeria is a strongly marked descendant of the 
Helicotoma or Ophileta type. Though the general aspect is widely different, the real 
differences are not so great as they appear on first sight, and, what is more important, 
they are rather easily accounted for. In Hisingeria the slit-band or keel has been 
reduced in prominence and moved inward from the outer edge of the upper side of 
the whorl to near the suture line, while the revolving strie, which as a rule are but 
ili developed in Helicotoma, have been strengthened and the outer basal angle 
somewhat extravagantly thickened. The last feature is perhaps the most striking 
peculiarity when compared with, for instance, Helicotoma planulata Salter, but in our 
_ H, subquadrata the outer basal angle is somewhat prominent, while in our H. 
marginata, a new species from the extreme top of the Lower Silurian, a similar 
feature is even more abruptly developed. Still, we doubt very much that the latter 
is In any wise an ancestor of Hisingeria planorbis, the real line of descent from 
Ophileta being, in our opinion, as yet undiscovered or unrecognized as such. 
Eccyliopterus, Remele, which we place in this family, has already been discussed 
in connection with Raphistoma on pages 935 to 938. The genus is a good one and 
includes shells with contiguous whorls similar in most respects to those of Helico- 
toma, and others in which they are more or less completely disconnected. The 
latter have usually been confounded with Hccyliomphalus, but as we have endeavored 
to show, the true position of the genus is nearer Ophileta and Helicotoma than 
Eccyliomphalus. The distinguishing character of Eccyliopterus lies in the remarkable 
development of the upper keel which projects beyond the surface of the whorls like 
a high collar. 
Genus OPHILETINA, n. gen. 
For remarks on this genus see page 1028. 
Only two or possibly three small species of this interesting genus are known. 
In these the whorls are rather slender, contiguous or partly free, coiled almost in 
the same plane, and either hexagonal or subquadrate in section. On the upper side 
and forming the outer edge there is a sharply elevated convex—or flat-topped—ridge 
which looks very much like a true slit-band, being covered with strongly recurved 
lines (lunulz) and terminating anteriorly in a well-marked notch. On the vertical 
outer side the lines of growth are bowed forward in the middle, on the lower side 
