ORDOVICIAN FAUNAS. 183 
different from the specimens here referred to LZ. micula. Pleuroto- 
maria micula was illustrated, but not described, by Hall, the speci- 
mens coming from the Trenton formation in Wisconsin. The species 
ras afterwards reidentified and described by Ulrich and Scofield in 
their Minnesota report, and it has been recognized as a rather common 
Trenton form in the Mississippi valley. he real status of L. sub- 
tilistriata still remains in doubt. It is possible that it is really a 
minute species, and that the large specimens illustrated for the species 
are specifically distinct from the minute specimens indicated in the 
description, and should be referred to L. micula. It is also possible 
that the small individuals mentioned by Hall are only the young of 
the larger one, and that the two supposed species, subtilistriata and 
micula, are one and the same, in which case the name swbtilistriata. 
having priority, would be the proper designation of the species. 
HORMOTOMA SALTERI Ulrich. 
Plate wN SS Big 29: 
eon Llormotoma saver) Wir Pal Minne pi lp. W016. ple 70; 
figs. 44-51. 
Description.—Height 12 to 40 mm.; apical angle 24° to 25°. Volu- 
tions nine or ten in large individuals, rounded, with a central, flattened 
or slightly concave, revolving band, which is bordered on each side by 
a delicate, raised line; not recognizable on the internal casts. Suture 
simple, deep. Lines of growth fine, bending strongly backward from 
the suture to the band, and beneath this curving very strongly forward 
again. Aperture nearly circular, the outer lip deeply notched at the 
revolving band. 
Remarks.—This species has been separated from the common H. 
gracilis (Hall) by Ulrich because of its greater apical angle, the 
typical form of H. gracilis having an apical angle of but about 
18°. In all other respects the two species are essentially alike, and 
the specimens now referred to H. salteri have always previously 
been referred to H. gracilis. The species is rather common in the 
Trenton lmestone of New Jersey in some localities, and in none of 
those observed is the apical angle less than 24°, and in but few is it 
