What is "mandaloceratidae"

Mandaloceratidae is a family in the nautiloid cephalopod order Discosorida, from the Middle and Upper Silurian characterized by short, essentially straight shells referred to as breviconic, typically with a faintly exogastric shape produced by the profile of the body chamber. Apertures vary from round to T-shaped, with a long narrow, ventral, hyponomic sinus for the maneuvering funnel. Siphuncles are commonly central or subcentral with generally broad, expanded, segments and usually thin connecting rings.

The narrow hyponomic sinus, which is an opening for the water-jet funnel by which the animal could move, much as with modern squid and octopods, points toward the lower or ventral side. The cross bar of the "T" or the round part of the aperture through which the animal could extend itself is located closer to the back or dorsal part of the shell.