54 MOLLUSCA. 
deeply impressed suture, each one usually somewhat excavated above, 
the outer one conspicuously so below the carina; beneath rounded ; 
covered with fine, radiating striz, with occasionally a larger, rib-like 
one. Aperture sub-rhomboidal, the lip horizontal above, inflected 
externally, and rounded below in conformity to the calibre of the 
whorl. A single lamina revolves within, on the penultimate whorl. 
Diameter one-fifth of an inch; length of axis one-thirtieth of an 
inch. 
Inhabits Tahiti. Couthowy. 
A most singular discoidal shell, resembling Planorbis vortex. 
Figure 50, the shell above; 50 a, the shell below, and 50 4, late- 
rally, enlarged ; 50 c, natural size. 
HELIX D#DALEA (Gould). 
Testa parva, discoidea, rubro-castanea, fusco tessellata, costellis radi- 
antibus acutis confertis scabra, subtus acetabuliformis : spira anfrac- 
tibus ad sex arcté volutatis, duplo altioribus quam latis, ad peripheriam 
rotundatis, infra haud planulatis ; sutura impressa: apertura an- 
gusta, verticalis, lunata; fauce lamellis nonis volventibus instructa, 
quorum quatuor ad anfractum penultimum, uno ad columellam, 
duobus ad basim, tribus ad labium dispositis. 
Helix dedalea, Goutp; Proceed. Boston Soc. Nat. Hist., u. 173. 
Sept. 1846. Expedition Shells, 21. Pretrrer; Monog. Helic., 1. 186. 
SHELL small, discoidal, flat above, deeply concave beneath, rough, 
with crowded, sharp, radiating rib-strie. Colour reddish-brown, 
checkered with dusky. Whorls about six, closely revolving, twice 
as high as wide, periphery rounded ; suture well impressed. Beneath, 
all the whorls present their rounded edges so as to form a cup-shaped 
cavity. Aperture vertical, lunate, twice as high as wide, and extend- 
ing one-third below the plane of the spire : fauces with nine revolving 
lamelle, of which four are on the penultimate whorl, two at the base 
of the lip, and three within the outer lip; also the trace of another 
on the pillar. 
