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tering lateral teeth, near the hinge. Ligament internal, inserted in the 



cardinal pits. 









M. gigantea, 



M. australis, 



M. lactea, 



M. Brasiliana, 



' Spengleri, 



' violacea, 



' abbrcviata, 



' donacina, 



' striatella, 



' fasciata, 



' ovalina, 



' depressa, 



' carinata, 



' turgida, 



« alba, 



' lilacea, 



' helvacca, 



' plicataria, 



' sol id a, 



' trigonella, 



' grandis, 



' rufescens, 



' castanea, 



' deltoides, 



' stultorum, 



' maculata, 



' rufa, 



' crassatella 



' maculosa, 



' subplicata, 



' squalida, 



' alata. 



' strarainea, 



' triangularis, 







2. Shells not gaping at the sides. 



Crassatella. Shell inequilateral, suborhicular or transverse; the valves 

 close; two rather diverging, cardinal teeth, and a pit by the side of them. 

 Ligament internal, inserted in the pit of each valve; lateral teeth, none; or 

 obsolete. 



C. Kingicola, 

 ' donacina, 

 ' sulcata, 



C. rostrata, 

 ' glabrata, 

 ' subradiata, 



C. contraria, 

 ' cuneata, 

 ' erycincea, 



C. cycladea, 

 ' striata. 



Erycina. Shell transverse, rather inequilateral, equivalve, rarely gaping; 

 two unequal, diverging, cardinal teeth, having a pit between them; and two 

 oblong, compressed, short, entering, lateral teeth. Ligament internal, fixed 

 in the pits. 



E. cardioides. 



DIVISION II. Ligament showing itself on the outside, or being double; 

 has one internal, the other external. 



Ungulina. Shell longitudinal or transverse, rounded on the upper part, 

 subequilateral; valves not gaping, beaks eroded. A short and rather bifid 

 cardinal tooth in each valve; with an oblong, marginal, adjoining pit, divided 

 in two by a contraction. Ligament internal, inserted in the pits. 



U. oblonga, U. transversa. 



Solenimya. Shell equilateral, equivalve, transversely oblong, the ex- 

 tremities obtuse; the epidermis shining, and extending beyond the margin. 

 Beaks not prominent, scarcely distinct. One cardinal tooth in each valve, 



