with Descriptions of the new Species. 



371 



H. Ma'ctra Linn. 



Shell ovate trigonal, subangular at each end. Cardinal teeth two in each 

 valve ; the front tooth of the left valve, and both of the right valve, thin, 

 compressed ; hinder of the left valve trigonal, folded. The lateral teeth 



distinct, anterior and posterior. Siphoned inflection ovate, distinct. Liga- 

 ment external, in a more or less oblique triangular groove, separated from 

 the cartilage pit by a distinct shelly septa. 



A. The lateral Teeth subequal, laminar, thin, moderately distant from the Urn- 

 bones and the Hinge Teeth. Hinge marginal, double-edged. 



* Lunule and Lozenge smooth. 



1. Mdctra glauca ; M. helvacea Chemn. 



2. Mdctra stultorum Linn., var. white. 



3. Mdctra maculuta Lam. 



** Lunules concentrically grooved. Lozenge smooth. 



4. Mdctra discors Gray. Shell ovate, trigonal, rather solid, ventricose, 

 white. Umbones nearly close, with two diverging reddish lines. Lozenge 

 rather flattened, rugulose, margined by slightly raised lines, with two 

 or three raised concentric lines. Ligament very small. 



Inhabits . 



Much the habit of a Mulinia, but grooved in front. 



*** Lunule and Lozenge concentrically grooved. 

 § Shell thin. Umbones rather separate. Ligament diverging. 



5. Mdctra tumida Chemn.; M. tiirgida Lam. The anterior tooth T-shaped; 

 the anterior part arising from the middle of the front side of the hinder 

 part. 



6. Mdctra gr an dis Lam. (fg- 30.) 



7. Mdctra orndta Gray. Reddish, pale-rayed, and white-dotted. Um- 

 bones bright red. 



Inhabits China. 



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