259 
tliG BiiddlG, wliicli is ratliGr broad in comparison with tliG sizo of tliG sIigII. 
TIig umbilicus sGoms to mo doop and fnnnGl-sbapGd. TIig siirfacG is perfectly 
smooth. 
Dimensions. — The length of this small shell does not exceed three 
millimetres, and its breadth three and a half millimetres. It may possibly 
be only a young individual of a larger species. 
Delations and Differences.— McCoy has described a small species, 
very like this, under the name P. Icevis. It differs by being more discoidal, 
more depressed, and especially by having a relatively much narrower band, also 
by the less elevated position of this band in the spire, which last circumstance 
allows it to be seen on all the whorls, while it is visible only on the last whorl 
in P. helicinceformis. 
Horizon and Localities. — A single specimen was found in the brown 
argillaceous limestone at Burra good. 
Genus — MUBOIIISONIA, d'ArcUac and de Verneuil. 
Murchisonia trifilata, J. D. Dana. 
Dleurotomarla trijilata, J. D. Dana, 1847, Am. Journ. Sci., (2), p. 151. 
„ Morrisiana, Idem, 1849, Geol. Wilkes’ U.S. Explor. Exped., p. 706, pi. 8, 
fig. 16 (fig. 15 exclusa, non E. McCoy). 
This is an elongated conical shell of moderate size, composed of seven 
or eight spiral whorls, with a triple keel, the top one of which is obsolete and 
follows the rather deep suture. The two inferior keels serve to limit the band 
of the sinus, which is grooved and covered with small plates of growth. The 
upper part of the last whorl is convex. The shell has no umbilicus ; its 
aperture is oblong ovate, and its slit seems to have been deep. The whole 
surface is ornamented with fine, slightly arched, oblique, rather deep and 
irregular strise. 
Dimensions. — This pretty shell can attain a length of about two 
centimetres, and a diameter of from nine to ten millimetres. Its spiral angle 
is about 51°. 
Relations and Differences. — Dana, probably not having good specimens, 
has confused this with the Rleurotomaria that McCoy dedicated to Morris. 
2 M 
