This genus was erected by Case for several dozen specimens from Early Eocene (Ypresian) of Mississippi. He included them as dasyatids.

Referred to as rhomboid when viewed occlusally (Case 1994, Kent 1999), these teeth are six-sided and, depending on position, may be laterally compressed (anterior per Case) or expanded (lateral).

The teeth are small (to 4mm per Case) and are characterized by a transverse, dome-like, cusp which rises high from the base. Viewed laterally, the lingual face of the cusp is more erected than the labial. Viewed lingually, there is a deep depression running mesio-distally above the base of the crown. The lower lingual face has enameloid ridges running basio-apically.

The roots are short, the nutrient groove relatively wide and deep, and when viewed basally, the roots are smaller but similar in profile to the crown. They are positioned lingually, and the laterally elongated teeth may have a third (medial) lobe. The lingual faces of each lobe have a mild depression, but no margino-lingual foramina have been noted.

Fig. 1 - Meridiania convexa
hgt = 1.7, wid = 2.8, dep = 2.1 mm
Potapaco Member, Nanjemoy Formation, Virginia
From the collection of Mike Folmer