95 
hand of the sinus ; the sides adjoining this keel, each of which are equally 
prominent, are hardly arclied, and the surface is ornamented with delicate 
oblique more or less regular lines of growth. The anterior portion of the 
last whorl of the spire is concave. The columella is simple and slightly 
sinuatcd. The mouth is elongate and suh-rhomhoidal. 
Dimensions. — This species may attain a length of three or four 
centimetres. The transverse diameter of the last whorl of the spire cor- 
responds to about six- tenths of this dimension [length] . 
Relations and Differences.-— species has been confounded by 
d’Archiac and de Verneuil with the one Phillips has described under the 
name of Rostellaria angidata, from which it can easily he distinguished by 
its spiral angle and double keel, as I have had occasion to point out since 
1843. The Devonian species that the learned Professor of Oxford considered 
identical with the Carboniferous species I have just mentioned, and which he 
has described and figured under the name of Murchisonia angidata^ is just 
as different from the species in question. Indeed, instead of the two keels 
with which the body whorl of this form is ornamented, that of M. angulata, 
Phillips, has three well-marked ones, as the description and figure testify. 
Horizon and Locality . — A single specimen of this species has been 
found in the black limestone of the Yass District, associated with Discina 
alleghania, J. Hall. In Germany it is rather common in the Middle Devonian 
limestone of the Pafrath District. In Belgium I have come across it in 
limestone of the same age at Vise and Mmy, where it is rare. 
2. Muuchisonia turris, L. G. de Koninch. 
PL IV, Pig. 5. 
Shell elongated, having the appearance of a cone hollowed in the form 
of a screw, composed of twelve to fifteen spiral whorls which are angular, 
and the spiral angle only 13°. The spire is divided into two unequal portions 
by the band of the sinus, which, as well as being rather narrow, is bounded 
by two carin®, the posterior of which is larger, with a more prominent 
margin than the anterior, and Corresponds to the larger portion of the spire ; 
this portion is also a little more convex, but the surface of each is ornamented 
v/ith slight lines of growth, a little oblique. The aperture of the mouth is 
suD-semicircular. The columella has no umbilicus. 
' Pal. Foss. Cornwall, p. 101, pi. 30, fig. 189. 
