50 MAZATLAN BIVALVES 



'f- 77. DONAX NAVICULA, Hani. 



Proc. Zool. Soc. 1845, p. 15. -C. B. Ad. Pan. Shells, p. 278. 



no. 456. Eve. Conch. Icon. pi. 4, sp. 18. 



A charming little species, both for its extreme beauty, and 

 the distinctness of its characters. Shell singularly swollen, 

 margin gibbous, scarcely shewing crenations beyond the edge 

 at the anterior end : clothed with very glossy epidermis, be- 

 neath which are obsolete striae. Ordinary colour greenish 

 white, gradually assuming darker shades, often beaked with 

 orange, generally more or less rayed, and ending in dark 

 orange chesnut. Inside from white to fawn, ending in deep 

 purple. Often (not always) with two streaks of purple within 

 and without, bounding the lunular and posterior areas. It 

 varies in the greater or less elongation, and in the ventral mar- 

 gin which is sometimes incurved. One monster was found, 

 shewing more prominent striae, long '44, lat. '9, alt. '29. 



Ordinary size "3, '66. .23. 



SmaUest '2, '43, '14. 



Hob. Gulf of Kicoyia, Cuming. Panama, E. Jewitt, C. B. 



Adams. Mazatlan ; not uncommon ; L'pool Col. 



Tablet 202 contains 5 specimens, most common variety, very 

 pale. 203, 3 darker, tipped with orange. 204, 3 darker, 

 slightly rayed. 205, 4 normal state, rather dark, indistinctly 

 rayed. 206, 3 sp. rays more evident, tipped with orange. 207, 

 3 sp. brownish orange. 208, 3 the same deeper. 209, 3 rich 

 dark brown. 210, the monster. In all, 28 specimens. 



FAMILY 

 GENUS MACTEA, Lin. 

 78. MACTRA EXOLETA, Gray. 



r- 



Mag. Nat. Hist. 1837, p. 372. Eve. Conch. Icon. pi. 4, sp. 16. 

 This exquisitely beautiful species is recognized easily by 

 the angle at the posterior side, and by the great prolongation of 

 the flattened anterior margin, which rises into a sharp keel 

 dividing the lunular portion. It diifers from M. alata, Speng. 

 ( = M. carinata, Lam. teste Eve. ?) in having no laminar keel 

 on the posterior angle. The epidermis which is deciduous, 

 but closely adherent when fresh, only shews striae of growth, 

 and gradually fades away towards the umbos which are always 



