PLACENTICERATID®. 191 
increase in complication of outlines of the lobes and saddles and their large 
size. This phylogerontic character is also accompanied, as stated above, 
by loss of ornamentation and retention throughout life of the compressed, 
involute, smooth volutions of the neanic stage. 
The living chambers are persistently one-half of a volution in length, 
whether occurring in depressed or compressed shells or in dwarfs, and the 
apertures, so far as seen, have a short, blunt rostrum and low, broad lateral 
crests. 
Grossouvre’s careful descriptions and exceptionally fine figures of 
the different forms included under the name of Placenticeras syrtale show 
that while there exists in France and Germany a series closely parallel 
to that of guadalupe, sancarlosense, newberryi, pseudosyrtale, and planum in 
this country, all of the European shells present differences showing that 
the evolution of the modifications was distinct in France. The geroutic 
stages show a greater tendency on the part of the inner lines of nodes to 
grow farther out on the lateral zones and approximate to the venter, and 
the venter not only flattens out to a plano-convex outline, as in some 
American species, but also in a subsequent gerontic substage, as in 
P. grossouvrei and milleri, becomes more or less concave. This is due to 
the increasing size of the tubercles of the median line on the borders 
of the venter after the disappearance of the ventral lines of earlier stages. 
Kossmat® sums up the literature of the genus Placenticeras and its 
allies. The type of the genus Buchiceras is erroneously considered as a 
species of Schloenbachia. Schloenbachia is a genus with normal outlines to 
the sutures, a decisive keel with channels or smooth bands on either side, 
and more or less sigmoidal, prominent, well-developed cost, the aperture 
having a long, pointed rostrum correlating with the keeled venter. The 
development is also very distinct from that of any of the Pseudoceratites of 
the Cretaceous. In preceding pages, B. bilobatum is jomed with other 
related species, and the differences of the series to which it belongs can be 
more readily seen. Kossmat’s strictures with regard to my own work on 
this group are just and most of bis objections well founded. His reference 
to baldwi Keyserling, as the probable radical of Placenticeras may be 
correct. At any rate there are some facts that favor this. The sutures 
are similar to those of Placenticeras. The young of this species certainly 
aSiidind. Kreidef.: Beitr. Pal. und Geol. Osterreich-Ungarns und des Orients, Vol. IX, 1895, p. 171. 
