umbones

[MYTILUS INCRASSATUS] Shell nacreous, thick, somewhat inflated, marked with concentric lines of growth; anterior margin arched accuminate; posterior rounded, somewhat dilated; umbones acute.

Report of the North-Carolina Geological Survey. Agriculture of the Eastern Counties: Together with Descriptions of the Fossils of the Marl Beds 1858

-- (Fig. 236.) Shell small, thick, triangular, oblique; ribs strong and crenate; umbones acute.

Report of the North-Carolina Geological Survey. Agriculture of the Eastern Counties: Together with Descriptions of the Fossils of the Marl Beds 1858

[ASTARTE CONCENTRICA] Shell small, thick, triangular, compressed, concentric; furrows close and regular; umbones acute, recurved; margin crenate.

Report of the North-Carolina Geological Survey. Agriculture of the Eastern Counties: Together with Descriptions of the Fossils of the Marl Beds 1858

-- (Fig. 221.) Shell inflated, concentrically striate, anterior side angulated; umbones prominent, incurved; margin smooth; lumule cordate.

Report of the North-Carolina Geological Survey. Agriculture of the Eastern Counties: Together with Descriptions of the Fossils of the Marl Beds 1858

Shell solid, surface marked by numerous concentric lines of growth, obliquely cordate; posterior margin produced; anterior short; umbones recurved, lunule cordate; pallial line sinuated; margin crenulated.

Report of the North-Carolina Geological Survey. Agriculture of the Eastern Counties: Together with Descriptions of the Fossils of the Marl Beds 1858

Page 285 umbones incurved, distant; ligament area crossed by transverse lines.

Report of the North-Carolina Geological Survey. Agriculture of the Eastern Counties: Together with Descriptions of the Fossils of the Marl Beds 1858

[ARCA LIENOSA] lines of growth distinct, giving a striate appearance; the ligament area is marked by strong lines diverging from beneath the umbo; umbones distant; inside margin strongly sulcate or ribbed.

Report of the North-Carolina Geological Survey. Agriculture of the Eastern Counties: Together with Descriptions of the Fossils of the Marl Beds 1858

The shell is orbicular, white, with depressed umbones, and the margins are either smooth or only finely crenulated; hinge teeth 2 -- 2, laterals 1 -- 1, muscular impressions rugose; anterior, elongated and within the pallial line; umbanal area with an oblique furrow.

Report of the North-Carolina Geological Survey. Agriculture of the Eastern Counties: Together with Descriptions of the Fossils of the Marl Beds 1858

[CRASSATELLA GIBBESH] "Shell somewhat triangular, thick, concentrically furrowed; buccal side rounded; anal side somewhat beaked, angular, with a longitudinal ridge; umbones incurved; lunule somewhat excavated."

Report of the North-Carolina Geological Survey. Agriculture of the Eastern Counties: Together with Descriptions of the Fossils of the Marl Beds 1858

The young verrucosus has sometimes one or two broad interrupted green lines over the middle of the umbones.

Transactions of the American Philosophical Society 1771