10 The American Geologist. Joly, 1894 
retained replacements in silica. These silicious fossils are 
differently preserved, many of them are simple replacements 
of the shell in all its parts, without the filling of the inter- 
spaces; others have the silicious shell retained in connection 
with a silicious filling of the internal cavities, though the 
depositions are discrete and were evidently successive; by 
the breaking of the external shell the internal filling can be 
readily removed. Again, the silicification of the shell has 
frequently been continued into an internal thickening which 
may more or less completely fill the chambers, though usually 
leaving the siphonal cavity unclosed. In this material there 
are twenty-four examples which retain the protoconch ; many 
of these are not mere parts of mature individuals, but the 
young shells themselves. These specimens represent at least 
two distinct species of Bactrites, one a long, styliform shell, 
with decidedly elliptical cross-section and comparatively dis- 
tant septa ; the other a more rapidly expanding shell, sub- 
circular in cross-section and with closer septa. • The former, 
I am disposed to believe, includes the specimens from this 
horizon which have been described as Orthoceras and Coleo- 
lus aciculum Hall, probably also 0. aciculoides Clarke, and 
some portion of the specimens which, in the absence of deter- 
minative material, have been referred to <K pacator Hall. The 
latter is a species which is hardly distinguishable from Sand- 
berger's B. gracilis. Not only does it possess the contour and 
proportions of the specimens described by him,* but it also 
bears the characteristic surface sculpture over all the earlier 
shell growth, "sehr feine schrag zum Riicken laufende Lin- 
ien," and upon the later growth, especially the body chamber 
are "verwaschene, wellig-heraustretende, schrage, breite Quer- 
rippen auf den Seiten, welche zu einer stumpfwinkeligen Dor- 
salbucht zusammenneigen." Without entering into a more 
detailed account of the specific features of these specimens, it 
will serve our purpose to regard them as representing B. 
gracilis Sandh.f 
Protoconch. This is a bubble-shaped body, frequently a 
*Verstein. des rhein. Schicht. Syst, Nassau. \>. 130, pis. \i. figs. 9a, 
1>: xii. figs. 2, a !': wii. (i^'s. 5, a-e, 1856. 
|-This species occurs a1 a corresponding horizon on the Iberg and else- 
where in Germany. 
