ADDITlONAIi NOTK.S ON THK OAMHHIAN OF CAPE fOUirON 
399 
faint impressions of vascular trunks on each side of the callus runninji^ 
forward. 
The dorsal valve has its greatest height near the middle, and has an 
appressed umbo, close to the» hinge line ; the lateral margin, in the pos 
terior half are re volute. Interior . — A median septum starting near 
the hinge line, extends across the middle of the valve to nearly one- 
third from its front ; it is widest in the middle and fades away to a 
point in front. On each side of it is a vascular grove, the pair radi, 
ating from near the umbo and extending nearly to the front margin 
they are nearly as far apart at the front as half of the width of the 
valve. Another pair of such grooves, about half as far apart as these , 
are faintly impressed on each lateral slope of the valve. The visceral 
cavity is faintly marked out by striated lines in the pqsterior half of 
the valve, and has an irregular arched front, projecting near median 
septum towards the front of the valve. Faint vascular stria* are 
visible on the median area towards the front of the valve. Some 
examples from the horizon E.3/> have a shorter septum, and show 
the position of the central and lateral muscles closer to the hinge 
line. These shells are more o-blate. 
Sculpture . — This is only known near the side of the valve, where 
it consists of fine, closely set, more or less tuberculated ridges, parallel 
to the margin. 
Size . — Length and width equal, 7 mm. Depth of the ventral 
valve about f of a millimetre ; that of the dorsal 1 mm. 
Horizon and locality . — All the horizons from E. 3a to E. 3e, ex- 
cept E.3cf, at Dugald Brook, Escasonie, N. S. 
The Acrotheles of E.3c are much corroded, and do not show 
the characters well ; they are mostly moulds from which the shell has 
been exfoliated. One ventral shows well the hollow behind the hinge 
area, and the foramen. 
Examples from the assises E.3e. have in the ventral valve quite a 
small tubercle in front of the foramen ; the visceral callus extends 
half of the length of the shell, and at each side in front are sometimes 
seen pits of the adductor muscles ; on each side of the callus a groove 
runs out toward the front margin. Some examples show a median 
and two lateral septa in front of the callus. Often the shell has an 
even surface to the margin, but frequently there are a few strong con^ 
centric ridges that mark stages of growth. 
