366 ANATINID.B. 



Genus PHOLADOMYA, Sowerby. 



Siphons united. Foot with a small, bifurcate pedal ap- 

 pendage behind. 



Shell transversely oblong, thin, white, translucent, equi- 

 valve, ventricose, gaping at both sides, anteriorly short and 

 rounded, posteriorly produced and sub-truncate, pearly in- 

 side ; surface of valves with radiating ribs. Hinge with a 

 small, elongated, triangular pit, and an obscure lamellar 

 tooth in each valve ; cartilage short, external, marginal. 

 Pallia! impression with a large sinus. 



Ex. P. Candida, Sowerby, pi. 97, fig. 1, I, a, 1, o. 



As shown by Owen, the animal of Pholadomya has the 

 mantle-margins united, with the exception of an aperture 

 for the foot, and a siphonal and an anal orifice, and there is, 

 besides, a fourth small, circular aperture at the under part 

 of the siphons; the gills are single on each side, with the 

 outer lamina prolonged dorsally, and there is an accessory, 

 bifurcate foot. One recent species only is known, P. Can- 

 dida, which is found occasionally on the shores of the 

 Island of Tortola, in the West Indies, after hurricanes, 

 being thrown up, it is conjectured, from deep water, by the 

 violence of the wind and waves. Several extinct forms, as 

 Goniomya, Homomya, Platymya, and Arcomya, closely 

 allied to Pholadomya, have been described by M. Agassiz 

 in his " Etudes critiques." 



