AND DESCRIPTIONS OF NEW SPECIES. 97 



York. Its natural situation seems to be between the cariosus (Say), 

 and complanatus (Solan.). It has the capaciousness of the former, and 

 somewhat of the outline of the latter. 



Unio Incurvus. Plate XIII. fig. 27. 



Testa ovato-rhomhed, transversa, iniBquilaterali; valvulis antice crassis, postice 

 tenuibus; natibus rugosis, pi'ominenlibus incurvisque; dentibus cardinalibus ele- 

 vatis cristatisque, lateralibus longis et subcurvis; margaritd alba et iridescente. 



Shell ovate-rhomboidal, transverse, inequilateral ; valves thick anteriorly and thin 

 posteriorly; beaks rugose, prominent and incurved; cardinal teeth elevated and 

 crested; lateral teeth long and slightly curved; nacre pearly white and iridescent. 



Hab. ***. From Gibraltar, Mrs Mawe. 



My Cabinet. 

 Diam. 1, Length 1-4, Breadth 2.1 inches. 



Shell ovate-rhomboidal, transverse, slightly inflated; substance of 

 the shell thick and w hite anteriorly, thin and iridescent posteriorly ; 

 beaks prominent, large, incurved and rugose, with small concentric un- 

 dulations : ligament rather short and thick ; epidermis yellowish brown ; 

 rays oblique and green ; cardinal tooth elevated, crested and divided in 

 the left valve, in the right simple and recurved ; lateral tooth long, 

 slightly curved and enlarged at posterior termination ; anterior cica- 

 trices distinct ; posterior cicatrices confluent ; dorsal cicatrices situated 

 on the under part of the cardinal tooth ; cavity of the beaks wide and 

 angulated ; nacre white on the anterior, and iridescent on the posterior 

 portion. 



Remarks — This shell, although it possesses no very striking char- 

 acter, cannot be placed with any American or exotic described species 

 with which I am acquainted. It was sent to me by Mrs Mawe with 

 the locality "from Gibraltar" on the label, and I have little doubt but 

 that it came from some neighbouring African river. It certainly does 

 not belong to any described European species. It bears more resem- 

 VoL. IV.— Z 



