1899.] Geology and Paleontology. 559 
region of the Northeastern Alps, and that north and south of this band 
the basins were unproductive or. analdainic. Among the aldainic 
basins, that of the Northeastern Alps showed by far the most ancient 
fauna, and all those in the aldainic zone to the westward exhibited less 
of the primitive or radical Psiloceran forms, Thus it is shown that 
even taking the minute sub-divisions of the Lower Lias, those hereto- 
fore supposed to be of the same age, by studying the life histories 
of the species and following out their genesis, it may be shown that 
they belong really to a successive series whose relations in time can be 
determined by the relations of their faunas. 
This memoir is issued in one of the volumes of the Smithsonian 
Contributions to Knowledge, and also in the series of the memoirs 
of the Museum of Comparative Zoology, Cambridge, Mass. It is illus- 
trated by fourceen plates, four of which are arranged phylogenetically. 
Plate XIV. is here reproduced as Plate No, XIX. 
EXPLANATION OF PLATE No. XIX. 
Tue three preceding plates do not illustrate the biological relations of the 
Arietidz as a whole with sufficient clearness, and this plate has been added 
been placed in what may be deemed its true position, between the plicatus 
stock and the levis stock; otherwise, the arrangement is the same. The 
resemblances of the morphological equivalents in each series can be readily 
seen by following the forms along horizontal lines from left to right. The 
independence of the origin of these representative forms can be studied by 
following up the series in vertical lines, which represent descent. Toa 
large extent, also, the more obvious differential characters which distinguish 
each series become appreciable by the same process. 
Psil. planorbe, var. leve, Fig. 1; var. plicata, Fig. 2. 
Schlot. catenata, Fig. 3, is the radical of this series. 
Schlot. angulata, Fig. 4, is evidently a transition to the next species. 
Schlot. charmassei, Fig. 5. The whorl is more involute, but the degene- 
rate characters of compression in the whorls and shallowing of the abdomi- 
nal channel begin to appear. 
Schlot. boucaultiana, Fig. 6. The involution has attained its maximum, 
and the degeneration of the pila and channel is well marked. 
Weh. curviornatum (sp. Wah.), Fig. 7, is undoubtedly distinct from 
Schlot. angulata, and is one of the radicals of this series 
Wek. haploptychum (sp. Wah.), Fig. 8. 
Weh. toxophorum (sp. Wah.), Fig. 9, is a degenerate shell, having com- 
pressed whorls, and pilz crossing the abdomen, as in the proximate radical 
Weh. curviornatum,. It is, however, more involute. 
