Pelecypoda 31 



from the observer, the hinge hgament will be behind the beaks. The 

 valve on the right side is the right valve and one on the left side is 

 the left valve. Examination of a smgle valve shows the umbo point- 

 ing to the left when the left valve is seen from the outer side, and 

 toward the right when the inner side is observed. The reverse is true 

 of these genera whose umbos are directed posteriorly. The pallial 

 sinus is always nearest to the posterior end of the shell, and the 

 greatest length is generally behind the umbos. 



White and light-colored bivalves sometimes show a pink or pur- 

 plish tint, deepest on the inner surface of the valves. Heilprin noted 

 this staining and attributed it to some process of ferric oxidation. 

 Since the atypical coloration is usually seen in the shells of living, 

 sand-burrcwing bivalves — not in gasteropod shells — it is suggested 

 as perhaps due to the purple secretion of Tethys or some tubicolous 

 worm. The purple-colored secretion has been observed to settle in 

 the saucer-shaped depressions in the sand about the projecting 

 siphons of Cyrtopleura costata whose shells oftenest show the pink 

 tint. It is possible that the purple secretion which accumulates in 

 these depressions is taken through the siphons into the mollusk's 

 mantle cavity, and either stains the inside of the shell by contact or 

 by the process of excretion. Dead shells of both univalves and bi- 

 valves sometimes acquire such a stain, probably by contact with the 

 purple secretions of various marine creatures which settle in de- 

 pressions where shells are also apt to lodge. 



Class TELECYPODA 



Order PRIOJfODESMACEAio 



Family SOLEMYIDAE 



The distribution of the Solemyidae is from Nova Scotia around 

 peninsular Florida and to the West Indies. Their distinguishing 

 feature is the heavy, glossy periostracum which extends well be- 

 yond the free margins of the shells in distinct scallops. This family 

 is not well known to collectors. Perry has seen but three specimens 

 in many years. 



^" Gr., prion, a saw; desma, ligament, saw-toothed. 



