Foerete.] 
294 
May 1, 
are never very evident except along the ridges of the radiating 
striae. 
All of these forms agree in having no beak rising conspicuously 
above the general surface of the shell or extending beyond the car- 
dinal margin ; indeed, the curvature at the beak is nothing more 
than a continuation of the curvature of the remainder of the shell. 
Internally they all agree in having the muscular scars of the dorsal 
valve strongly defined along the median region of the shell by two 
raised ridges, slightly diverging anteriorly. Anteriorly the limi- 
tation of the muscular scars is less distinct, and laterally it may be 
quite faint. Even when well defined the lateral limitations of the 
scars are not linear and sub-parallel but strongly curved. In this 
they agree well with the typical forms of Leptcena sericea , Sowerby. 
1. Leptcena glabra, Shaler, from Ellis Bay, Anticosti, has an av- 
erage length of 11 mm. and a corresponding width of 21 mm., or 
slightly more. The convexity of the ventral valve is almost if not 
quite equal to that of Leptcena sericea , Hall, from the Clinton of 
New York. The beak extends a little beyond the hinge line and 
is not broad. The surface of the shell is marked by numerous, 
very fine, radiating striae, ten or eleven in a width of 1 mm., in- 
terspersed with which at quite narrow intervals are others, singly, 
and but moderately larger, never prominent as in forms of Leptcena 
transver salis, so that the general surface appears in effect quite 
smooth as the name implies. It is evidently a form intermediate 
between Leptcena sericea and A. transver salis, but until the interior 
is better known it may perhaps be best correlated with Leptcena 
transver salis, as a variety glabra, on account of the more distinct 
beak and the greater convexity. 
2. Leptcena sericea, Hall, from the Clinton green shale at Roch- 
ester, New York, has a length equal to .6 the width. The anterior 
margin of the shell is rounded, often almost semi-circular, rounding 
evenly into the lateral margins and forming a more acute angle with 
the cardinal margin. The ventral valve is strongly convex, the 
beak curving slightly beyond the cardinal margin and having but 
moderate breadth. The dorsal valve is less curved than the ven- 
tral, concave, leaving considerable space for the viscera. The sur- 
face is marked by fine, radiating striae, intercalated with which at 
quite regular intervals are others, much broader and strongly ele- 
vated, so that the spaces occupied by the intervening finer striae 
often appear slightly concave. 
