GASTROPODA. 843 
Stenotheca unguiformis.] 
casts, both from Minneapolis, they are faintly indicated. Muscular scars not 
observed.* Length of aperture 20 mm.; width of same 13.5 mm.; length of shell 
from apex to posterior margin 26 mm. These dimensions in a large and a very 
small specimen are respectively about 29, 16 and 42 mm., and 4.5, 3 and 5.5 mm. 
The large specimen has suffered from pressure so that the width is less than 
normal. 
Aside from the fact that it grew to a much larger size, this species resembles S, 
rugosa var. levis Walcott (Tenth Ann. Rep. U.S. Geol. Surv., pl. uxxiv, figs. 5, 5a) 
more closely than it does any Lower Silurian shell known to us. 
Formation and locality.—Stones River group, Vanuxemia bed, Minneapolis, Minnesota, and Beloit, 
Wisconsin. 
Collections.—Geological and Natural History Survey of Minnesota; University of Minnesota; Univer- 
sity of Wisconsin. 
Museum Register, No. 715. 
2 STENOTHECA UNGUIFORMIS, 7. sp. (Ulrich.) 
PLATE LXI, FIGS. 42—44, 
Shell unguiform, acuminate-ovate from above, rounded posteriorly, narrow in 
front where the apex curves more or less strongly downward, sometimes nearly to 
the plane of the aperture and projects considerably beyond the anterior margin; 
aperture horizontal, ovate, usually much more broadly rounded behind than in 
front. Surface with distinctly elevated, regular, sublamelliform, concentric lines, 
from 0.2 to 0.6 mm. apart, the distance between them increasing with growth; 
crossing them very fine radiating lines; test rather thick; surface of cast smooth. 
Three specimens have the following dimensions: length of aperture 6.5, 10.2 and 
11.5 mm.; width of same 5.8, 9 and 9.1 mm.; length of shell 7.7, 12.8 and 15 mm.; 
hight of same 3, 4.5and 6mm. Old specimens have thick edges and are relatively 
longer than medium and young examples. This is because the increase of the 
shell, after a certain stage, takes place principally at the posterior border. For the 
same reason the beak appears more strongly incurved in old shells. 
This species is clearly distinct from all previously described patelloid shells. 
There may be some doubt about the generic position, the anterior hight being less 
than it should be ina true Stenotheca. The Cambrian S. ? elongata Walcott, however, 
exceéds our species in that respect, while in its younger stages it is decidedly like 
some of the forms referred to S. rugosa by the same author. We believe, therefore, 
that we cannot be far wrong in placing it under Stenotheca. 
Formation and locality.—Upper beds of the Trenton group, between Burgin and Danville, Kentucky. 
Collection.—K. O. Ulrich. 
*Mr. Sardeson says of the muscular scars that they “are not distinct on the cast, but there appears to be a row of 
about 24 passing around the shell from 2 to5 mm. above the lip of the aperture.” 
