149 
between them. The present is smaller and proportionally more 
slender^ and the spire is more attenuated. 
Note. — Bulla fldviatilis, noh., seems to he no other than the very 
deceptive young of our common Planorhis. 
Ancylus tardus. — Shell conic depressed : apex behind the 
middle obtuse, rounded, inclining backward but not laterally : line 
from the apex to the posterior tip rectilinear ; line from the apex 
to the anterior tip arquated : aperture oval, not distinctly narrowed 
at one end. 
Length, a little over three-twentieths 4-25 ; breadth, one-tenth 
of an inch. 
Differs from A. rivularis, nob., which has the apex leaning 
towards one side, and the aperture narrower at one end. It is less 
elongated than fliiviatilisy Drap., which has an acute and laterally 
inclined apex. 
It inhabits the Wabash River. 
[No. 6. Transylvania Journal of Medicine, vol. 4, p. 525, etseqq. 1831.] 
[The descriptions of these species were afterwards repeated fn the 
“American Conchology.” For the sake of greater convenience they 
will he found under that head. They were not included in Mrs. Say’s 
“ Descriptions.” — Ed.] 
Astarte.— -Shell suborbicular, generally transverse, equivalve, 
insequilateral, closed entirely ; hinge with two strong, distinct, di- 
verging teeth on one valve, and on the other two very unequal 
teeth and a lateral obsolete one ; ligament exterior ; muscular im- 
pressions two, and a minute one above the posterior impression, 
almost confluent with it ; impression of the mantle simply arquated, 
distinct. 
* [No description already included in my reprint will be repeated here, 
but any additional remarks, &c., will be given. — ^B d.] 
UnIO INTEREUPTUS; 
‘ ‘ NEXUS, 
Unio glebulus. 
DBCLIVIS, 
Unio lapillus 
[No. 7. American Conchology.] 
[Am. Con., part 1, 183^.] i 
