Shell inequivalve; punctuate, rather rugose, front deep, rounded; attached by a considerable portion of the ventral valve; beak slightly incurved; deltidium small and depressed. The ventral valve is flattened on its under side. Its interior is surrounded by an elevated, slightly granulated margin. Under the deltidium are seen two raised oval processes, separated by a longitudinal septum, which occupies the greater length of the shell. The exterior of the dorsal valve is rugose and flattened. The interior possesses a narrow, thin, punctuated margin, immediately succeeding which is a ridge of single granulations, which are stronger towards the frontal margin, gradually disappearing as the ridge passes upwards. Springing from the centre of this granulated ridge is a septum, slightly tapering from its base, on either side strongly serrated, between which is a central longitudinal groove. The septum occupies nearly the whole height allowed by the cavity of the shell, and divides it to nearly three-fourths of its length. From the top of the septum there are thrown off two extremely delicate lamellæ, forming a loop which curves downwards towards the front of the shell, where they bifurcate, and are then again united to the shell at its inner sides. Above the septum and attached lamellæ a band occurs, forming a bridge over the visceral cavity. This is united to the granulated ridge, which thus completely surrounds the inner portion of the valve.