338 AXEL A. OLSSON 



7. Shell smaller and thinner (perhaps a form of asper). 



D. rostratus 



d. Shell broad, subquadrate, depressed, the beaks decidely posterior 

 in position. 



8. Posterior, submedian groove weak, not forming a marginal tooth. 

 Coloration varied. 



D. panamensis 



e. Shell elongated, subtrigonal, strongly convex, the posterior side short, 

 the umbonal keel sharp. 



9. Color usually a deep mahogany brown, the anterior surface smooth 

 and polished, the deeply depressed or flattened posterior slope finely 

 and uniformly sculptured. 



D. carinatus 

 BB. Posterior side less sharply truncated, the umbonal keel obtuse or 

 rounded. 



f. Shell small (15 mm. or less), obtusely subovate. 



10. Color usually white or gray, with some purple staining. Umbonal keel 

 rounded. 



D. obesus 



g. Shell generally larger, elongately subtrigonal. 



ga. Surface smooth except for indistinct fine radials, the interradial division 

 merely lined, not pitted or punctated. 



11. Color white, cream or light violet, plain or rayed, the interior generally 

 with a purple stain. Peruvian. 



D. peruvianus 



gb. More heavily sculptured, the radial riblets or threads more distinct, 

 their separating intervals finely pitted. 



12. Shell small, the surface with strong cancellated and radially pitted 

 sculpture. 



D. ecuadorianus 



gba. Shell larger, the sculpture consisting mainly of pitted radial interspaces. 

 Punctatostriatus group 



13. Radial riblets strong and distinct over whole surface, their intervals 

 deeply punctated, especially anteriorly, cross-striated elsewhere. 

 Mexican. 



D. punctatostriatus 



14. Shell with less convexity, the radials finer, their intervals more closely 

 punctated. 



D. contusus 



15. Surface smooth, porcellaneous, white, the radials fine. Shell with 

 strongly humped umbones and more inflated valves. 



D. mancorensis 



Donax rostratus C. B. Adams Plate 61, figures 1-lb 



Donax rostratus C. B. Adams, 1852, Ann. Lyceum Nat. Hist. New York, vol. 5, pp. 502, 



545, No. 457. Panama.— Turner, 1956, Occas. Papers on Mollusks. Mus. Comp. 



Zool., vol. 2, No. 20, p. 82. Type lost. 

 Donax granifera Deshayes, Morch, 1855, Proc. Zool. Soc. London, p. 353. Hab. - - -? — 



Reeve, October, 1854, Conch. Icon., vol. 8, Donax, pi. 7, fig. 43. Hab. - - -? 

 Donax graniferus Deshayes, Sowcrby, 1866, Thes. Conch., vol. 3, Donax, p. 307, No. 12, 



pi. 280, fig. 18. 

 Donax curtus Sowerby, 1866, Thes. Conch., vol. 3, Donax. p. 308, No. 20, pi. 308, fig. 



20 Caraccas Bay, West Colombia. 



