Exogastric

Preoperatively and intraoperatively it is difficult to distinguish benign and malignant lesions; all may demonstrate a mixture of intramural, endogastric and exogastric appearances.

Vexing are two exogastric genera of the Simard limestone.

I interpret Mellopegma as exogastric and separate it from Peel's (1991) class Helcionelloida because of its extremely narrow aperture with uniformly ventrally curved lateral margins.