GASTROPODA. 859 
Cyrtolites.] 
But this will not do, for it would be nothing less than ignoring most palpable 
facts. We must return to the original type, C. ornatus, and restrict the genus to 
species possessing essentially the same generic peculiarities. After the characters 
mentioned in the first sentence of the preceding paragraph, which brings us 
down in the identification of the genus to four or five similarly constructed types, 
these peculiarities consist of (1) the subquadrangular cross-section of the whorls, 
(2) the simple and sharp edged or minutely serrated character of the dorsal 
carina, (3) the total absence of a slit-band and (4) the pattern of the surface 
markings which, with a single exception, differs from that of all other beller- 
ophontids. The second and third of the features is shared by Oxydiscus, but as 
the latter has more numerous and more compressed volutions, a much deeper 
apertural emargination and slit, and lines of growth only, there is little trouble 
in separating it from Cyrtolites. Conradella is distinguished by its slit-band and 
remarkably long apertural slit, by the rounded or cordate section of its whorls, 
and by its strongly imbricating and wavy surface lamelle; Porcellia has a long 
slit like Conradella, rounded volutions, the inner ones unsymmetrically coiled, and 
different surface markings. For comparisons with Cyrtolitina, which of all the 
Bellerophontide at present seems to be the nearest, see remarks on that genus 
(some pages hence). 
Such strong resemblances are to be traced between casts of species of Cari- 
naropsis and Cyrtolites, that, despite our strong assertion to the contrary on a later 
page, we would really not be surprised if future discoveries should prove that the 
two genera are related genetically. At present, however, the origin of that genus 
is enveloped in the greatest obscurity. As to Cyrtolites, it may have sprung from 
Cambrian Stenotheca. 
The species remaining under the genus as restricted are not many, and all (six) 
about which there is no doubt are illustrated in this work. Four of the six are 
described as new. Of the other American species that have been referred to the 
genus, C. compressus Conrad, C. dyeri Hall, C. elegans Miller, C. imbricatus Meek & 
Worthen, and C. pannosus Billings, belong to Conradella; C. magnus Miller and C. 
cristatus Safford, to Oxydiscus; C. nitidus Ulrich, to Cyrtolitina; C. subcarinatus 
Emmons, probably to Carinaropsis. C. filosus Emmons and C. trentonensis Conrad are 
Cephalopoda; while the remaining forms, C. desideratus Billings, C. expansus Hall, C. 
gillanus White & St. John, C. sinuatus Hall & Whitfield, and C. sinwosus Hall, are too 
little known to be placed with anything lke certainty. Of European species that 
have been referred to Cyrtolites perhaps none really belong there. C. delanouei 
(hlert, and C. orbiculus Lindstrém doubtless belong to Oxydiscus, to which we are 
inclined to refer C. discus Lindstrém as well, although it has a distinct slit-band 
