GASTROPODA. 1023 
Euomphalide.] 
above and below to the median keels, passing apparently over these and then across the concave central 
space with a slight backward curvature (see fig. 56, pl. LXX); aperture subquadrate, very slightly pro- 
duced below; umbilical perforation extremely minute or wanting. . 
The small carina just beneath the suture line distinguishes this species from S. prisca. 
Tf Salter’s figure (Joc. cit.) is correct, then the Canadian types of the species must have a wider apical 
angle than the Minnesota and Wisconsin specimens above described. The angle of the illustration in 
question is about 22°, while it is not over 15° in our examples. Weare, however, inclined to doubt the 
accuracy of the Canadian illustration, especially since Billings, after giving the apical angle of his Hunema 
prisca at “about 12°,” says that his species is distinguished from EZ. pagoda only by the absence of the 
upper carina. 
Formation and locality.—Black River group, Pauquettes rapids, Ottawa river, Canada ; Phylloporina 
bed, near Cannon Falls, Minnesota; ‘‘ Upper Buff limestone,” near Beloit, Wisconsin. 
Collections.—University of Wisconsin; HE. O. Ulrich. 
Family HUOMPHALID A. 
This important family, according to our opinion, is to be viewed as an off-shoot 
from the same early type in which both the Raphistomide and Pleurotomariide also 
originated. It is to be expected, therefore, that, although some of the earliest forms 
of the family underwent very rapid and strongly marked changes, the majority are 
decidedly like their contemporaneous cousins. For the same reason it is evident 
that for some of the “majority” it is difficult to decide whether they had best be 
regarded as Euomphalide or as members of one of the other families. With our 
present limited knowledge of their progenitors, it is perhaps impossible to arrive at 
positive conclusions. 
Already in the Calciferous and Quebec groups, which contain the earliest fully 
known representatives of the present subclass, we find unequivocal members of 
the family. Of them we may mention Eccyliomphalus intortus, distans and canadensis 
of Billings, E. (Caularops) lituiformis Whitfield, Straparollus quebecensis Billings, and 
Euomphalus caleiferus Whitfield. The Kccyliomphali are clearly of the line of 
development which found its continuance in ZL. angelini Lindstrém, of the Swedish 
Lower Silurian, H. undulatus Hall, of the Stones River group, and our Trenton 
species, H. subrotundus; and possibly its culmination in the Upper Silurian shells 
from the island of Gothland, described by Lindstrém as Hwomphalus triquetrus and 
E. gotlandicus.* Concerning this line of development, we are fully convinced that 
it stands in only very remote genetic relationship to the large group of Upper 
Silurian Carboniferous species which is typified by Euomphalus pentangulatus, the 
derivation of the latter group from the equally ancient types of Ophileta, being, as 
we shall show presently, very easily demonstrated. 
The immediate progenitor of the Calciferous Eccyliomphali, we conceive to 
have been a form like our Ec. contiguus with contiguous, though perhaps narrower, 
* Walcott’s Eccyliomphalus devonicus (Monog. U. S. Geol. Sur., vol. viii, p. 187; 1885) may represent a continuation of this 
type, but his specimen is so imperfect that it is impossible to arrive at satisfactory conclusions respecting it. 
