GASTROPODA. 1027 
Euomphalida.] 
layer. Thus, while the upper keel terminates anteriorly in a deep notch and the 
growth lines curve backward strongly both from above and below in approaching 
the keel in Helicotoma, they pass almost directly across the whorls in these Euomphali. 
In passing over the keel they are but little, if at all, deflected, but a broad backward 
sweep on the lower side of the whorls produces a slight obliquity of the aperture. 
In stating the differences in the direction of the lines of growth of the Carbon- 
iferous and Lower Silurian shells just compared, we were careful to say, “the 
surface of the outer layer,’ because we have reason to believe that the markings of 
the inner layer are not the same as those of the outer. We have before us a 
remarkable specimen of an undescribed Huomphalus from the oolitic limestone of 
the Upper Coal Measures at Kansas City, Missouri. The species is closely related 
to and perhaps not specifically distinguishable from the Chester group shell to which 
Meek and Worthen have given the name JH. planidorsatus. There is no doubt then 
about its genetic relations. The specimen in question has the external layer of the 
shell peeled off in patches so as to expose the inner layer. Both layers show lines 
of growth very distinctly, and it was in comparing their respective directions in the 
region of the upper keel that we met with a surprise. On the outer layer, namely, 
the strizs pass almost straight from the suture to the keel, beyond which they turn 
first very gently forward and then more strongly backward into the broad basal 
sinus. The inner layer seems to be composed of short overlapping laminz, the 
edges of which impressed themselves upon the internal cast as closely arranged 
parallel grooves. The latter, instead of being direct like the lines of the outer layer, 
curve backward strongly in passing over the region of the keel, thus indicating a 
very decided >-shaped notch in the lip, which must, however, have been confined 
to the inner layer of the shell. Immediately beneath the keel the test is thick 
enough to produce a faintly concave instead of convex band on the interior cast. 
After seeing this specimen, the important question arises, do not the same 
conditions pertain to all the similarly carinate Euomphali? Unfortunately we have 
no positive data bearing upon the question, although we have seen specimens of 
other species in a similar state of preservation; but the specimen described is the 
only one showing any sign of transverse markings on the inner surface of the shell, 
the casts in every other instance being quite smooth. Still, the Kansas City speci- 
men proves that a notched aperture may really exist in species of Huomphalus 
exhibiting no external sign of its presence, and this fact is, to say the least, worthy 
of being remembered. 
In addition to the euomphaloid types discussed on the foregoing pages, we 
distinguish three others, two of them under new names, the third described and 
named Eccyliopterus by Remele. 
