As Arca melanoderma:

Montijo Bay, Rep. Panama (Lowe). Type 155627 ANSP.; paratype in Lowe coll. Panama City on reef beyond "French Plaza (Pinchot Exped.).
The irregularly oblong shell is strongly inequilateral, slightly inequivalve, the left valve projecting very narrowly beyond the right throughout the ventral margin; moderately plump; rather thin; white, under a black periostracum which is bristly and, especially at the ends, densely lamellose in the intercostal intervals. The hinge is slightly curved, meeting the posterior margin at an angle and curving into the rounded anterior margin. Posterior end much higher than the anterior, oblique, nearly straight. Ventral margin arcuate. The rather small beaks are in front of the anterior fourth of the length, contiguous, with no ligamental area between them. The sculpture consists of about 35 ribs, a little wider than their intervals, most of them divided by a groove except near the beaks; some weak, low, and very inconspicuous, irregularly developed concentric ridges pass over the intervals and in some places the ribs also. The small teeth are vertical in the middle, strongly- oblique posteriorly, the anterior series short, with about 6 to 9 irregular teeth. Valve margins deeply fluted Length 31 mm., height 21.5 mm., diam. 15.9 mm.
This species seems close to Area brevifrons Sowb., but it has many more ribs, the valves are less unequal, and the posterior end is less oblique.'