148 BULLETIN OF THE 
appears that this species is not a Zonites, as orignally described, but rather a 
Microphysa, like M. Lansingi and M. Ingersolli. With the former it shares 
the peculiarity of having a ribbed jaw and aculeate marginal teeth to its lingual 
membrane. 
The jaw has over 19 ribs of the! same type as those of MZ. Lansingi (see Pl. II. 
Fig. O). A portion only of the jaw is figured. 
The lingual membrane (Pl. II. Fig. N) has four laterals on each side of the 
central tooth. 
Microphysa Ingersolli, Branp. (p. 173.) 
Ogden, Utah. 
Onchidella Carpenteri, W. G. Brxnrey. (p. 179.) 
Body oblong, extremities bluntly rounded: upper surface regularly arched ; 
below, quite near the edge, the border of the mantle is readily 
distinguished ; most of the under surface is occupied by the 
broad, distinct locomotive disk: the body is uniformly smoke- 
colored ; the four specimens received vary from 5 to 3 mm. in 
length. | 
Onchidium Carpentert, W. G. Binn., Proc. Phila. Ac. N. Se., 1860, p. 154. Land 
& Fresh-W. Sh. N. A., Part I. p. 808, Fig. 545 (1869). 
Unfortunately omitted from Vol. V. The locality, Cape San Lucas, is doubt- 
ful. It is so referred, probably by mistake, in the volume of Land and Fresh- 
water Shells of North America, quoted above. There is no jaw, which renders 
still more peculiar the presence of one in O. borealis; on this account, I place | 
the genus in Agnatha in the catalogue offered with this. The dentition is as 
in O. borealis (see Vol. V.). The upper margin of the base of attachment is still 
more prolonged in this species. 
Helicodiscus fimbriatus, Wretuersy. (p. 186.) 
Plate I. Fig. D. 
Shell light green color, discoidal or planiform, widely umbilicate, consisting 
of about five whorls, very gradually increasing in size. Aperture lunate, and 
oblique to the axis of the shell. Peristome subacute, slightly thickened, and 
darker than the rest of the shell, the outline somewhat sinuous when viewed 
from the side of the whorl. Suture deeply and regularly impressed. Um- 
bilicus exhibiting all the volutions. Whorls ornamented with from 6 to 8 
revolving ridges, terminating in a fringe-like projection of the epidermis, fol- 
lowing this arrangement. Two or three of these ridges on the upper side of 
the body whorl are often of such prominence as to give that portion of the 
