FAMILY 12. NAIADES. 119 



PI. LXXXIX. Fig. 10. 



Unio cariosus, Say, Enc. American Conch., pi. 3. f. 2. Lamarck. 



Anim. sans vert., new edit., vol. vi. p. 545. 

 Unio luteola, Conrad. 

 Unio ovatus, Valenciennes. 



HYRIA, Lamarck. 



Testa transversa, aequivalvis, inaequilateralis, oblique trigona, utrinque 

 auriculata, basi truncata, recta, epidermide olivacea induta, interne 

 margaritacea. Cardo dentibus duobus lateralibus elongatis in utra- 

 que valva; altero postico, quasi cardinali, multipartito ; altero antico, 

 lamellari, praelongo, in valva una bipartite Impressio muscularis 

 postica semper composita. Ligamentum externum, lineare. 



The shell of Hyria possesses many characters in common with that of 

 Unio, but may be nevertheless distinguished by its elongated lamellar 

 teeth. The auriculated or winged growth of the valves producing a 

 straight hinge-margin is also remarkable ; we refrain, however, from 

 citing this form as of generic importance, as it is nearly approached by 

 many of the Uniones and Anodontes. 



The shell of Hyria is described as being transverse, equivalve, inequi- 

 lateral, obliquely triangular, and so truncated at the base as to form a 

 straight dorsal or hinge margin. The valves are covered with an oliva- 

 ceous epidermis without, and are pearly within. The hinge consists of 

 two elongated lateral teeth, one on each side the umbo in both valves : 

 one is posterior, somewhat approaching to the form of a cardinal tooth, 

 and multipartite ; the other is anterior, lamellar, very long, and bipartite 

 in one valve, receiving the anterior tooth of the opposite valve. The 

 posterior muscular impression is always compound, and the ligament is 

 external and linear. 



