About Megasurcula carpenteriana (Gabb, 1865)
This description compares Bathytoma tremperiana to fully adult Megasurcula carpenteriana (originally referenced as Bathytoma carpentaria). B. tremperiana has a small shell; adult B. tremperiana average around 62 mm (2.4 inches) in length, while fully adult M. carpenteriana reach 90 to 110 mm (3.5 to 4.3 inches) in length. The shell of B. tremperiana is proportionally much heavier than that of M. carpenteriana. Its anal fasciole is more strongly constricted, and the appressed margin of its whorl does not approach the periphery of the preceding whorl as closely as it does in M. carpenteriana. The periphery of B. tremperiana's shell is often marked by a minutely beaded or undulate thread, and it sits more nearly midway between the sutures on the spire than the periphery of M. carpenteriana. In nearly all cases, the aperture of B. tremperiana is shorter than its spire, which is the opposite of what is seen in M. carpenteriana. This is a marine species that occurs from California, United States to Central Baja California, Mexico.
