560 The American Naturalist. [June, 
Weh. emmerichi (sp. Wah.), Fig. 10, shows a notably involute shell, 
with degenerate pila and compressed whorls. i 
al. tortile, Fig. 11, is the radical of this series. 
Cal. carusense, Fig. 12, has similar young to that of zortie below. 
Cal. nodotianum, Fig. 13, is very similar to carusense, but with more 
compressed whorls and better developed pilæ. 
Cal. cycloides (sp. Wah.), Fig. 14, shows compressed degenerate whorls. 
Cal. castagnolai (sp. Wäh.), Fig. 1 5, is more degenerate than the last, but 
slightly more involute. 
Cal. abnormilobatum (sp. Wäh.), Fig. 16, is a dwarfish and more degene- 
rate form than Castagno/az, but has more involute whorls, 
Cal. lagueum, Fig. 17, is an extreme form of this species, which approxi- 
mates very closely to a true sfiratissimum. 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. 
7 Verm. ophiodes, Fig. 20, exhibits the tuberculated pilæ of this species. 
Psil. aphanoptychum (sp. Wah.), Fig. 21, is one of the Plicatus stock of 
Psiloceras. 
Psil. kammerkarense (sp. Wah.), Fig. 22, shows the more involute and 
plicated form of this subseries, 
Psil. mesogenous (sp. Wah.), Fig. 23, is an involute shell belonging to the 
true Levis stock.1 
Arn. semicostatum, Fig. 24. 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. 
rn. hartmanni, Fig. 24, 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 channeled abdomens existed in this genus. 
Arn. bodleyi, Fig. 27, shows a slightly degenerate com 
is the terminal form of the sub 
pressed whorl, and 
ni. 
Arn. kridioides. 
series containing Hartman 
Fig. 28 gives a view of the transition between Arnio- 
ceras and the lowest species of Coroniceras. The smooth young straight 
pilæ and divergent side of the adult whorl are clearly shown. 
Cor. sauzeanum. Fig. 29 shows the later nealogic and ephebolic stages, 
having the peculiar divergent sides, flattened abdomen, and prominent 
1 Two subseries ought to have been shown here, but in trying to reduce the size of the 
e been placed in the same line. A similar liberty has been taken with 
f Caloceras and Arnioceras, but this does not interfere with the truthful 
Presentation of the general zoOlogical relations of the forms. 
