1112 The American Naturalist. [December, 
quite manifest, however, that both generic words ‚are taken from 
platys and stoma ; and that from these it was the intention of Con- 
rad to construct a correct generic term. In this attempt he used 
by mistake the connecting o, which is necessary in forming com- 
pounds from most Greek words, but which in the present instance 
was not called for, since the term is formed directly without the 
intervention of a copulatory vowel. For these reasons Conrad's 
and Klein's proposals cannot be regarded as distinct. 
Since it is clear, then, that Platystoma cannot be retained for 
the American group of Paleozoic gastropods, some other term 
must be adopted. Fisher® has taken advantage of the question- 
able validity of Conrad's name, and has recently proposed Dia- 
phorostoma for the same group, with Platystoma niagarensis Hall 
for his type. This writer places Hall's Strophostylus as a sub- 
genus under Diaphorostoma ; while Zittel” assigns Hall's section 
to a similar taxonomic rank, but under Platystoma. Had Con- 
rad's type of Platyostoma not been a form midway between the two 
extremes of a series forming the group Fisher's name might be re- 
tained, but the type of Strophostylus is congeneric with P. ventri- 
cosum ; and as this name is the next proposed it must be taken 
into consideration. Were it not for this fact two sections of this 
group of shells could be with great propriety made. As regards 
the term Strophostylus, it was established by Hall? in 1859 for 
certain shells closely related to Platystoma, but differing chiefly in 
having a slightly “twisted or spirally grooved columella." 
ecently a large series of the most important species of both 
Platystoma and Strophostylus was examined and the matrix 
carefully removed from the apertural portions of many of the 
shells. The structural features disclosed in the various forms 
show a relationship between the two established genera that was 
long suspected. It is well known that the type of Conrad’s genus 
— Platystoma ventricosum Con.—is a somewhat globose shell with 
a small spire elevated slightly and having the aperture broadly 
ovate. The inner lip is somewhat thickened and subangular 
* Man. de Conch., p. 756. 
? Handb. der Palæ., I. Band, 2 Ab., p. 217. 
® Palæ. N. Y., Vol. IIL, p. 303. 
