GENERA PRODUCTUS AND STROPHALOSI i. 
153 
little extension of the characters of Productus or of Strophalosia might 
include them; but while Strophalosia and Aulosteges remain dis¬ 
tinguished by such small differences, these forms also, I conceive, 
should be separated from the former, both on account of the ex¬ 
ternal differences and from the direction of the reniform vascular 
impression, which has been regarded as an important feature in the 
Productidse. These differences I consider as scarcely less important 
than those upon which the other subgenera have been separated; and 
from their external form and internal structure so nearly resembling 
Productus, I would propose for the Devonian species having narrow 
hinge-areas and small toeth and sockets, with reniform vascular impres¬ 
sions of the form of those illustrated, the name Productella. 
Sul»«*enii§ Productella (n. s.g.) 
Shells having the general form of Productus, but uniformly with a nar¬ 
row area on each valve, a foramen or callosity on the ventral area,* 
small teeth, and more or less distinct teeth-sockets. 
The reniform vascular impression, rising from between the anterior 
and posterior occlusor muscular impressions, curves gently outwards, 
and following a curvature somewhat parallel with the margin of the 
shell to below the middle of its length, is abruptly recurved, and the 
extremity turned a little backwards teminates about half way between 
the margin and the anterior extremity of the mesial septum. 
The cardinal process, seen from the inner side, is bilobed, and from 
the exterior side each of these divisions is usually bilobed. 
These shells differ from Strophalosia in the extremely narrow linear cardinal 
area, greater extension of the hinge-line, more extreme arcuation or ventricosity 
of the ventral valve in many or most of the species, and especially .in the direc¬ 
tion and termination of the reniform vascular impressions, which resemble those 
of Aulosteges and of some species of Productus. It differs from Productus in the 
constant presence of an area, hinge-teeth and sockets. 
* In the specimens affording the most satisfactory evidence of area, etc., the foramen is ojen; but in 
some specimens the impression only remains, and there is the appearance of a narrow indentation below 
the beak, so that it is impossible to determine whether the foramen has been open, or closed by a 
deltidium. 
[ Paleontology IV.] 
20 
