438 Avierican Seashells 



smooth, even at the blunt, posterior end. Only 2 color phases: yellowish 

 white or with weak purplish rays. Subsequent biological studies may show 

 that this common beach species is a subspecies or cold-water form of varia- 

 bilis. Young specimens of variabilis from several southern states look suspi- 

 ciously like this so-called species. 



Donax tu7indus Philippi Fat Gulf Donax 



Northern shores of the Gulf of Mexico. 



% to /4 inch in length, very obese, somewhat trigonal in shape, with its 

 beaks swollen and posterior end strongly truncate. Threads on the blunt 

 posterior end are heavily beaded, sometimes giving a cancellate appearance. 

 Narrow anterior end commonly with distinct, microscopic, distantly spaced, 

 incised, concentric lines. Color whitish with bluish, yellowish or pinkish 

 undertones. Rarely, if ever, rayed. Uncommon. Found in 2 to 3 feet of 

 water. 



Donax denticulatus Linne (pi. 3 op) from the southwest Caribbean has 

 been erroneously recorded from our shores. It is i inch in length and char- 

 acterized by 2 curved, low ridges on the posterior slope of each valve and 

 by microscopic pin-points on the sides of the valves, 



Donax striates Linne also a lower West Indian species is as large, but 

 characterized by a flat to slightly concave posterior slope which bears numer- 

 ous fine radial threads. 



Donax gouldi Dall Gould's Donax 



Plate 3iq 

 San Luis Obispo, California, to Mexico. 



Common jorm: % inch in length, fairly obese, truncate at the posterior 

 end where the beaks are located. Shell glossy, smooth, except for numerous, 

 microscopic, axial threads at the anterior end. Exterior cream to white with 

 variable color rays of light-tan. Margins of valves commonly flushed with 

 purple. Interior stained with purple or bluish brown. Common on beaches, 

 especially in the north. Kno\\^n locally as the Bean Clam. 



Small jorm: Yi inch in length, slightly more obese, without the color 

 rays in most cases. Common, especially in the south. 



Donax califorjiicus Conrad California Donax 



Plate 3ip 



Santa Barbara, California, to Panama. 



Up to I inch in length, narrowly pointed at both ends. Shell glossy or 

 oily-smooth with a tan to greenish-tan periostracum. Interior white or with 



