PROCEEDINGS OF UNITED STATES NATIONAL MUSEUM. 185 
aperture. Forward of the fold there is little and sometimes no accumu- 
lation of callus, the anterior end of the outer lip, where it joins the inner 
lip, being usually thin and more or less prominent when entire. There 
is, therefore, in unbroken shells a rather broad, short, more or less dis- 
tinct anterior canal, too broad and short to really deserve the name of 
canal, strongly recalling the corresponding part of Nassa. The anterior 
border of this short canal, however, is prominent, and not emarginate, 
as in Nassa. 
From the fact that the columellar fold upon these Carboniferous shells 
is distinct only within the aperture, and the latter is usually filled with 
the imbedding matrix, this distinguishing feature seems to have usually 
escaped notice. It has not always done so, however; both those emi- 
nent paleontologists, Professors Hall* and Geinitz,t having referred to 
itin published descriptions. Meek and Worthen also observed that the 
inner lip is usually provided with an obtuse revolving fold”; but none 
of these authors appear to have regarded that feature as ee such 
shells generically from those which are destitute of it. Mr. Conrad, 
however, so early as 1842, proposed the generic name of Plectostylus 
to include shells possessing this character, but that name was previously 
used by Beck for another group of mollusks. Mr. 8. A. Miller, also, in 
his Catalogue of American Paleozoic Fossils, refers the Macrocheilus 
halli of Geinitz to Soleniscus Meek and Worthen. In 1881 I deseribedé 
two similar species from the Carboniferous rocks of New Mexico, and 
also referred them to Soleniscus. 
Notwithstanding the conscientious accuracy which is apparent in all 
the work of those authors, I suspected that the anterior portion of 
Meek and Worthen’s type species of Soleniscus is not so prominent as ‘it 
is represented to be by the restored part of their figures. 
Applying to Mr. Worthen for permission to examine the type-speci- 
men, I learned that it was inaccessible, but he sent me for examination an 
authentic duplicate example. <A careful examination of this specimen 
satisfies me that the anterior portion of the shell in this species is only a 
little more prominent than it is in several of those forms which have been 
referred to Macrocheilus, and that that portion is not produced into a 
proper beak. Meek and Worthen’s figures show that the anterior portion 
of their type-specimen was broken off, and if the line of the restored part 
had been continued with the curve of the outer lip it would agree with the 
lines of growth which are observable upon the specimen sent me by Mr. 
Worthen. Moreover, their figure shows a prominence of the fold upon 
the inner lip which did not appear on the one just referred to until I 
had dug out the stony material which had filled the aperture. Their 
*Geolcgy of Iowa, 1858, Part II, pages 719 and 720. 
tCarbonformation und Dyas in Nebraska, 1866, page 6, Pl. 1, Fig. 7. 
{ Expl. and Sur. West of the 100th Merid., supp. to Vol. III, pp. xxviii and xxix, PI. 
IV, Figs. 4 and 5. 
