ORDOVICIAN FAUNAS. 165 
CTENODONTA LEVATA (Hall). 
Plate XI., Figs. 18-22. 
1847. Nucula levata Hall, Pal. N. Y., vol. L, p- 150, pl. 34, figs. 
1la-k. 
Ctenodonta levata, as described by Hall under the name Nucula 
levata, undoubtedly includes shells which belong to several distinct 
species. There are much greater differences exhibited among the 
several specimens illustrated by Hall which are referred to this species 
than among many of the species of the levata group of the genus 
Ctenodonta described by Ulrich. Apparently all of the small, pele- 
eypod shells having this general form were referred by Hall to a 
single species, and the exact value of C’. Jevata can only be determined 
when Hall’s original specimens are more thoroughly investigated. 
In the fauna of the Trenton limestone of New Jersey more or less 
imperfect specimens of what are clearly several small species of 
Ctenodonta are not infrequently met with, most of them agreeing 
more or less closely with one or another of Hall’s illustrations of 
C. levata. They are usually not in a proper condition of preservation 
for accurate identification or description, and although some of them 
resemble more or less closely some of Ulrich’s species of the genus, 
none of them can be specifically identified with any certainty. Under 
these circumstances, it is thought best to refer them all to C. levata, 
as Hall undoubtedly would have done at the time he established the 
species, at the same time keeping in mind that this name is a sort of 
eatch-all for these small, pelecypod shells, awaiting a thorough revi- 
sion of the genus. 
CLIDOPHORUS NEGLECTUS Hall. 
Plate XI., Fig. 16. 
189%. Clidophorus neglectus Ulrich, Pal. Minn., pt. II., p. 607, pl. 
42, figs. 20-25. 
Description.—“Shell transversely subelliptic, rather strongly con- 
vex; ends subequally rounded, the anterior generally a little narrower 
than the’ posterior; the outline of the latter, however, often exhibits 
