Adontorhina Berry, 1947

Barry, Peter J. & Mccormack, Grace P., 2007, Two new species of Adontorhina Berry, 1947 (Bivalvia: Thyasiridae) from the Porcupine Bank, off the west coast of Ireland, Zootaxa 1526, pp. 37-49 : 38-39

Genus Adontorhina Berry, 1947

Type species: Adontorhina cyclia Berry, 1947 Description. Shell small, fragile, compressed to orbicular; surface sculpture of smooth commarginal striae, radial sulcus reduced or lacking. Beaks prosogyrous, low on the dorsal margin. Periostracum thin, lightly straw coloured. Ligament mostly internal, set on a narrow sunken shelf posterior to the beaks. Hinge plate composed of two sections, both anterior and posterior to the beaks; without true teeth but with irregular granules varying between species from weakly to strongly expressed. All possess a single demibranch. Foot with heel, lateral pouches relatively small and undivided. Surface of lateral pouches has the appearance of arborescent tufts.

Remarks. The irregular granules on the hinge margin have only been reported in this genus. Indeed, when first discovered Berry (1947) recorded “I have been unable to find any described genus or species to which it can be referred”, owing to the uniqueness of the granular hinge. A large majority of the shells in the Thyasiridae have either edentulous hinges or underdeveloped tubercles instead of teeth ( Payne & Allen, 1991). Coan et al. (2000) separated the externally similar Adontorhina from Leptaxinus Verrill & Bush, 1898 , on the basis of the distinctive hinge. Scott (1986) remarked that there is wide variation in strength of expression of the irregular granules across the genus. While the granules on the hinge plate is the strongest character uniting the species of Adontorhina , all have a reduced sulcus, low umbones and the lateral pouches are undivided and not thrown into numerous lobes. The foot of each species is noticeably shortened with a deep sagittal groove.