Vedavati or Hagari river, mostly dry in the hot
season. Several parallel chains of hills, reaching an extreme height of
3800 ft., cross the district; otherwise it is a plain. The chief crops
are cotton and flax; the chief manufactures are blankets and cotton
cloth. The west of the district is served by the Southern Mahratta
railway. The largest town in the district is Davangere (pop. 10,402).
The town of CHITALDRUG, which is the district headquarters (pop. 1901,
5792), was formerly a military cantonment, but this was abandoned on
account of its unhealthiness. It has massive fortifications erected
under Hyder Ali and Tippoo Sahib towards the close of the 18th century;
and near it on the west are remains of a city of the 2nd century A.D.

CHITON, the name[1] given to fairly common littoral animals of rather
small size which belong to the phylum Mollusca, and, in the possession
of a radula in the buccal cavity, resemble more especially the
Gastropoda. Their most important characteristic in comparison with the
latter is that they are, both in external and internal structure,
bilaterally symmetrical. The dorsal integument or mantle bears, not a
simple shell, but eight calcareous plates in longitudinal series
articulating with each other. The ventral surface forms a flat creeping
"foot," and between mantle and foot is a pallial groove in which there
is on each side a series of gills. Originally the Chitons were placed
with the limpets, _Patella_, in Cuvier's _Cyclobranchia_, an order of
the Gastropoda. In 1876 H. von Jhering demonstrated the affinities of
_Neomenia_ and _Chaetoderma_, vermiform animals destitute of shell, with
the Chitons, and placed them all in a division of worms which he named
Amphineura. The discovery by A.A.W. Hubrecht in 1881 of a typical
molluscan radula and odontophore in a new genus _Proneomenia_, allied to
_Neomenia_, showed that the whole group belonged to the Mollusca. E. Ray
Lankester (_Ency. Brit._, 9th ed., 1883) placed them under the name
Isopleura as a subclass of Gastropoda. Paul Pelseneer (1906) raised the
group to the rank of a class of Mollusca, under von Jhering's name
Amphineura.

The Amphineura are divided into two orders: (1) the Polyplacophora, or
Chitons; (2) the Aplacophora, or forms without shells, _Neomenia_,
_Chaetoderma_ and their allies.

Order I.--POLYPLACOPHORA

[Illustration: FIG. 1.--Three views of Chiton.

A. Dorsal view of _Chiton Wosnessenksii_, Midd., show