272 THE DEVONIAN FOSSILS OF CANADA WEST. 
valve is then nearly flat. Length from two to three lines, width 
about the same. 
The above description applies to the more common form of this 
species. Larger individuals from six to eight lines in length are 
occasionally found, but they do not seem to be so numerous as the 
smaller ones. In these, the dorsal valve is divided along the middle 
by a narrow, rounded sinus, which extends from the front nearly to 
the beak; on each side the shell is convex, sometimes rather strongly 
tumid. The ventral valve broadly carinate along the middle. The 
following figures represent the largest specimens that I have seen in 
different views. 
Fig. 98. 
Centronella tumida 2 
There are some intermediate sizes, but not sufficient to make out a 
series connecting these large individuals with the smaller. Should 
these constitute a distinct species, I propose to call it C’. tumida. 
Locality and formation.—Oriskany Sandstone and Corniferous 
Limestone, County of Haldimand. Also at Rama’s Farm, near Port 
Colborne. 
Collectors.—J. De Cew, E. De Cew, E. Billings. 
CenTroneLua Hecate.—W. Sp. 
a 6 Centronella Hecate.—a. A specimen with 
i) the dorsal valve removed, shewing the loop, 
dy () j\/ which is covered with minute crystals of 
Fig. 99. silex. 6. Ventral view of another specimen. 
e. side view, d. dorsal view. 
Description.—Elongate, oval, or sub-rhomboidal ; apical angle from 
45° to 60° ; sides somewhat straight from the beak to about the mid- 
dle, where, making a rounded angle, they converge towards the front 
margin, which is somewhat truncate for about one-third the width. 
Ventral valve strongly but broadly carinate from the beak along the 
middle to the front, descending with a flat or gently convex slope to 
