324 MACLUREIDA—HALIOTIDA. 
Shell thin, symmetrical, horn-shaped or discoidal, with whorls 
more or less separate, keeled and sculptured. 
OCYRTONELLA, Hall, 1879. Shell ovoid, trumpet-shaped; volu- 
tions one or more in the same plane; apex minute, making about 
a single turn, and rapidly expanding beyond, peristome entire ; 
dorsum angular or subearinate; surface sculptured. C. mitella, 
Hall. Devon.; N. Y. 
Famity MACLUREID#. 
Maciurea, Lesueur. 
Etym.—Named after William Maclure, the first American 
geologist. 
Distr.—Fossil, 12 sp. Paleozoic; North America, Scotland 
(Ayrshire, M’Coy). MM. Loganti, Salter 1xxxii, 8,9). M. magna, 
Lesueur (lxv, 10). 
Shell discoidal, few-whorled, longitudinally grooved at the 
back, and slightly rugose with lines of growth; dextral side 
convex, deeply and narrowly perforated ; left side flat, exposing 
the inner whorls. Operculum sinistrally subspiral, solid, with 
two internal projections, one of them beneath the nucleus, very 
thick and rugose. 
This singular shell abounds in the “ Chazy” limestone of the 
United States and Canada; sections of it may be seen even in 
the pavement of New York. ‘We are indebted to Sir W. E. 
Logan, of the Geological Survey, Canada, for the opportunity 
of examining a large series of silicified specimens, and of figuring 
a perfect shell, with its operculum 7m sztu. It has more the 
aspect of a bivalve, such as Requienia Lonsdalii, than of a spiral 
univalve, but has no hinge. Many of the specimens are over- 
grown with a zoophyte, generally on the convex side only, rarely 
on both sides. 
“The Maclurea has been described as sinistral; but its oper- 
culum is that of a dextral shell; so that the spire must be 
regarded as deeply sunk and the umbilicus expanded, as in cer- 
tain species of Planorbis; unless it is a case conversely parallel 
to Atlanta, in which both shell and operculum have dextral 
nuclei. The affinities of Maclurea can only be determined by 
careful examination and comparison with allied, but less abnormal 
forms, associated with it in the oldest fossiliferous rocks ; its rela- 
tion to Euomphalus (p. 218) is not supported by the evidence of 
Sir W. Logan’s specimens.”— WoopDWakD. 
Famity HALIOTID &. 
Shell spiral, ear-shaped, with a greatly expanded, flattened 
body-whorl, and large basal aperture; dorsally perforated in a 
