The overall shape is trigonal. The anterior and ventral margins are rounded, and the posterior margin may be slightly truncated. The anterior dorsal margin is straight and forms a steep angle. The posterior dorsal margin is subconvex. The posterior half of the flank is slightly more inflated than the anterior half. The valves are thick-walled, inflated, equal in size and shape (equivalve), and there is no gape when they are closed. Sculpture consists of growth lines and thin, dense comarginal ribs covering the entire dissoconch. The lunule is teardrop-shaped, extends 3/4 of the anterior dorsal margin and is defined by a fine shallow groove. The umbones are prominent, inflated and anterior; the beaks also point slightly anterior. The escutcheon is not well defined.
The exterior is white or light tan with a dirty gray periostracum. The interior is also white.
The ligament is external, but slightly sunken; it extends half the posterior dorsal margin and is supported by nymphal ridges. The hinge plates of both valves are robust. On the left valve, there are three cardinal teeth: the anterior tooth (2a) is weak and lightly bifid, the central tooth (2b) is more prominent and not bifid, and the posterior tooth (4b) is not bifid and fused to the nymph. The anterior (2a) and central (2b) teeth are fused near the hinge plate, forming an inverted "V" shape. There is also one anterior lateral tooth (A2) on the left valve. On the right valve, there are three cardinal teeth: the anterior tooth (3a) is not bifid, the central tooth (1) may or may not be bifid, and posterior tooth (3b) is bifid. There are also two anterior lateral teeth (A1, A3) on the right valve. There is a weak ridge that runs parallel to the posterior margin on both valves, but it is more prominent on the right valve. The anterior and posterior adductor muscle scars are similar in area, but the anterior is more elongate than the posterior. The pallial sinus is rounded and extends to the middle of the nymph in length.
Catalog Number: USNM 215082
Collection: Smithsonian Institution, National Museum of Natural History, Department of Invertebrate Zoology
Locality: Maldonado, Uruguay, South Atlantic Ocean
- Holotype: Nautilus. 29(10): 113.
Similar to Pitar morrhuanus. Pitar patagonicus is distiguishable by its more trigonal overall shape and its more robust hinge plate and teeth. In addition, the anterior tooth (2a) on the left valve and central tooth (1) on the right valve may be bifid--which is not found in P. morrhuanus.