38 Mighels^ and Adams^ Descriptions of 



J. Ray, M. D., formerly of Eastport, now superintendent of 

 the Insane Hospital at Augusta, Me., and Mr. N. T. True, 

 Preceptor of the Academy at Monmouth, Me. 



THRACIA TRUNCATA. 



Plate IV. Fig. 1. 



T. testa parva, solida, per-inequilaterali, postice truncata, et striata : callo 

 nymphali producto. 



Shell small, white, rather solid, abruptly truncate posteri- 

 orly, very inequilateral ; surface Avith three regions ; the ante- 

 rior region separated from the posterior by an umbonial angle, 

 which extends from the beak to the lower extremity, marked 

 with numerous minute incremental striae ; posterior region 

 with the incremental striae distinct and very much crowded ; 

 areolar region narrow, with regular striae of growth ; epider- 

 mis thin, of a pale straw-color ; beaks small, that of the right 

 side moderately excavated for the reception of the left ; poste- 

 rior dorsal margin straight, descending abruptly to an angle 

 with the anterior, which is also straight, making an angle with 

 the inferior, which is moderately curved: anterior margin 

 regularly rounded ; anterior dorsal margin slightly curved ; 

 ligament rather large and prominent ; interior of a clear 

 white ; nymphaeal callosity not spoon-shaped, produced ; pal- 

 lial impression deeper than wide. 



Average length, ^75 inch ; height, ,5 inch ; width, ,29 inch. 



Cabinets of Bost. Soc. Nat. Hist., J. W. Mighels, and 

 C. B. Adams. 



Habitat. Casco Bay, Me., obtained in 1840, from stom- 

 achs of haddock. 



Remark. Although this shell is small, its solidity, quite 

 unusual in the genus, forbids the supposition that it is imma- 

 ture. It is remarkably distinct from other species in the dis- 

 parity of the anterior and posterior sides, whose length are as 

 eight to three. It must be regarded as exceedingly rare, 

 three or four years exploration having developed only four or 

 five specimens. 



