CHONETES. 
SIS 
GENUS CHONETES ( Fischee, 1837). 
The Genus Cponetes, having the general form of Strophodonta or 
Strophomena and LEPT.®NA,-is distinguished externally from those forms 
by the tubular spines on the outer margin of the ventral area; and from 
Productus by the manner in which these spines are disposed. In some 
species, however, in addition to these, the surface of the shell is studded 
with small spines as in Productus. Internally it has been shown by Mr. 
Davidson to possess characters which ally it with Productus; and it 
connects more nearly, by form and general features, the families of 
Strophomenid^e and Production. . 
In the ventral valve, the area is narrow but well-defined, with a 
distinct foramen which is partially closed by a pseudo-deltidium, and the 
remainder of the space is filled by a cardinal process from the opposite 
valve. In the bottom of the cavity there is a longitudinal median ridge, 
and on each side and close to it are the occlusor muscular impressions: 
the divaricator impressions occupy a wider space, and usually are not 
very well defined in their limits, though having the same general form 
and features as those of Strophodonta. 
In the dorsal valve, the teeth-sockets are well marked. The cardinal 
process is entirely unlike that of the preceding genera, being simple at 
its base, and bifid or grooyed at the extremity; while the lateral divi¬ 
sions usually reach nearly as far as the central portion of the process, 
and are separated from that by a groove more or less distinct. Sometimes 
the lateral or accessory lobes are distant from the extremity, and sepa¬ 
rated in like manner by a groove. 
In one or more of the slender forms of the process, these lateral lobes' 
are situated at some distance from the apex, and appear like minute 
processes on the sides. At its base, the cardinal process is continued in 
a slender median ridge. The double occlusor impressions are small, and 
from between them proceeds an elevated vascular marking which 
assumes a reniform shape; this being a distinguishing feature of the genus, 
which allies it with Productus. 
