SUMMARY PLATE XIV. 
The three preceding plates do not illustrate the biological relations of the Aietidee as a whole 
with sufficient clearness, and this plate has been added for the purpose of supplying the defi- 
ciency. ‘he series of Psiloceras has been placed in what may be deemed its true position, be- 
tween 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. ‘To a 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. 24, is evidently a transition to the next species. The artist has 
exchanged Fig. 4 with Fig. 24. 
Schlot. Charmassei, Fig. 5. ‘The whorl is more involute, but the degenerate characters 
of compression in the whorls and shallowing of the abdominal channel begin to appear. 
Schlot. Boucaultiana, Fig. 6. The involution has attained its maximum, and the degen- 
eration of the piles and channel is well marked. 
Weeh. curviornatum (sp. Wiih.), Fig. 7, is undoubtedly distinct from Schlot. angulata, and 
is one of the radicals of this series. 
Weeh. haploptychum (sp. Wih.), Fig. 28. The artist has exchanged Fig. 8 with Fig. 28. 
Weeh. toxophorum (sp. Wah.), Fig. 9, is a degenerate shell, having compressed whorls, 
and pile crossing the abdomen, as in the proximate radical Wah. curviornatum. It is, however, 
more involute. 
Weeh. Emmerichi (sp. Wih.), Fig. 10, shows a notably involute shell, with degenerate 
pile and compressed whorls. 
Cal. tortile, Fig. 11, is the radical of this series. 
Cal. carusense, Fig. 12, has similar young to that of tortile below. 
Cal. Nodotianum, Fig. 13, is very similar to carwsense, but with more compressed whorls 
and better developed pile. 
Cal. cycloides (sp. Wiih.), Fig. 14, shows compressed degenerate whorls. 
Cal. Castagnolai (sp. Wiih.), Fig. 15, is more degenerate than the last, but slightly 
more involute. 
Cal. abnormilobatum (sp. Wih.), Fig. 16, is a dwarfish and more degenerate form than 
Castagnolai, but has more involute whorls, 
Cal. laqueum, Fig. 17, is an extreme form of this species, which approximates very closely to 
a true spiratissimum. This figure is therefore placed to the right, and under Verm. spiratissimum. 
Verm. spiratissimum, Fig. 18, shows typical form, with but slight channels. 
Verm. Conybeari, Fig. 19, shows normal untuberculated variety, with stout whorls and 
deep channels. 
Verm. ophioides, Fig. 20, exhibits the tuberculated pile of this species. 
Psil. aphanoptychum (sp. Wih.), Fig. 21, is one of the Plicatus stock of Psiloceras. 
Psil. Kammerkarense (sp. Wih.), Fig. 22, shows the more involute and plicated form of 
this subseries. 
Psil. mesogenos (sp. Wiih.), Fig. 23, is an involute shell belonging to the true Levis stock." 
Arn. semicostatum, Fig. 4. The figure represents the nearly full-grown shell; but if 
the keel were absent, the smooth whorls of, the young would closely resemble the adult whorls 
of Psil. planorbe, var. leve. The artist has exchanged Fig. 4 with Fig. 24. 
Arn. Hartmanni, Fig. 25, exhibits young and adult characters like those of the preceding. 
Arn. tardecrescens, Fig. 26, belongs to another subseries of forms than that in which it 
is placed, but it serves to, show that quadragonal whorled shells with channelled abdomens 
existed in this genus. 
1 Two subseries ought to have been shown here, but in trying to reduce the size of the plate the forms have 
been placed in the same line. A similar liberty has been taken with the subseries of Caloceras and Arnioceras, but 
this does not interfere with the truthful presentation of the general zoological relations of the forms. 
