GENERA OF SHELLS. 37 



cation or sinus, which seems to receive a portion of 



the ligament. 



(a.) Cardinal tooth short, thick, not crested, and substriated. 



U. sinuala, elongata, crassidens, Peruviana, rariplicata, 

 purpurata, ligamentina, obliqua, retusa, rarisulcatd, coarc- 

 tata, purpurascens, brevialis, rhombula, carinifera, georgina, 

 clava, recta, naviformis, glabrata, rotundata, httoralis, semi- 

 rugala, nana, delodonta, sulcidens. 



(b.) Cardinal teeth short, compressed, raised, and often 

 crested. 



U. rostrata, pictorum, Batava, corrugata, nodulosa, vari- 

 cosa, granosa, depressa, Virginiana, luteola, marginalis, 

 augusta, manca, spuria, australis, anodontina, suborbiculata. 



JV. American. U. ridibundus, monodonta, undulatus, abrup- 

 tus,phaseolus, tetralasmus, dehiscens, interruptus, globulus, 

 declivis, lapillus, camptodon, lugubris, radiatus, ovatus, cari- 

 osus. nasutus, cylindricus, subtentus, plicatus, rectus, torsus, 

 mytiloides, rnetanever, scalenius, cornutus, verrucosus, tuber- 

 culatus, gibbosus, cuneatus, ventricosus, siliquoideus, trian- 

 gularis, parvus, iEsopus, calceolus, lanceojatus, donaci- 

 formis, ellipsis, irroratus, lacrymosus, ater, rubiginosus, 

 heterodon, sulcatus, planulatus, circulus, multiradiatus, occi- 

 dens, securis, iris, zigzag, patulus. 



Hyria. Shell equivalve, obliquely triangu- 

 lar, eared, truncated at base, and straight. 

 Hinge with two short teeth ; one posterior or 

 cardinal, divided into numerous, diverging 

 portions, the interior of which are smallest ; 

 the other anterior or lateral, lamellar, very 

 long ; ligament external, linear. 



The hyria is distinguished from the unio, by its gen- 

 eral form, and by the cardinal tooth, particularly that of 

 the right valvCj w^hich is divided into numerous lamel- 



