104 
AUG. F. FOEESTE 
Onychochilus abruptum (Foerste) 
Paleopupa abrupta Foerste, Geol. Surv. Ohio, Pal., 7, 1893, 
p. 556, pi. 37A, fig. 21 a, b. 
The genus Onychochilus was proposed by Lindstrom in 1881, 
in his Silurian Gasteropoda of Gotland, three species, Onycho- 
chilus physa, On. reticulatum, and On. cochleatum being described 
by him in the order named, the latter doubtfully referred to the 
genus. Of these the first named, Onychochilus physa, here is 
regarded as the type. 
The specific name physa indicates the sinistra! curvature of 
the spire of the type species, a feature shared by all three species 
described by Lindstrom, and also by the peculiar gasteropod 
described by me under the generic term Paleopupa. The choice 
of the name Paleopupa as a generic term for a sinistral shell is 
unfortunate, since the Brassfield species so designated could not 
have been ancestral to any form of Pupa. Its resemblance to 
Pupa ends with its rapid apical expansion, followed by a much 
slower expansion along the last volution. Nothing is known of 
its surface ornamentation. 
In Onychochilus physa the aperture is obliquely rounded, the 
lower margin being distinctly angulated. There is no trace of 
an umbilicus. The surface striation is transverse. In Onycho- 
chilus reticulatum the angulation at the base of the aperture is 
even more pronounced. Vertical sections show that the umbili- 
cal passage through the axial part of the shell has been closed by 
a callous deposit. The surface is ornamented by both transverse 
and revolving striae, readily seen under a lens. In both species 
the rate of increase in size is more even than in Paleopupa dbrupta, 
and in the latter species no angulation of the base of the aperture 
was noted, but this part was not well preserved in the specimens 
studied. 
Nothing appears to be known of the relationship of Onycho- 
chilus, and the term does not appear in Zittel-Eastman’s Text- 
book of Paleontology. 
