Honjo to K?iow American Seashells 81 



the last traces of flesh, the radula may be soaked in a saturated solution of 

 potassium hydroxide (KOH) for a few minutes. A solution of common lye 

 will do as well. Animals whose flesh has been hardened by a preservative will 

 have to be carefully boiled for a few minutes or soaked overnight in KOH 

 or lye. Small specimens may be dropped whole into this alkaline solution 

 if only the radula is desired. Transfer the radula successively to several 

 watch-glasses of clean water in order to rid it of all traces of KOH. The 

 radula may then be placed in one or two drops of water on a clean, glass 

 microscope slide and, by observation under the dissecting microscope, a few 

 teeth may be teased apart with fine needles. Leave some of the ribbon intact 

 to show the relative position of the teeth. Add a square cover slip for study 

 under the compound microscope. In w^ater mounts such as these, stains are 

 usually unnecessary. This temporary preparation may be permitted to dry 

 for a day, the cover slip gently lifted, a few drops of euporol or mounting 

 medium added, and the cover slip replaced to make a permanent shde. Some 

 workers prefer to go from water to eosin stain to ninety-six percent alcohol 

 and then to euporol, but this is an unnecessary elaboration. There are also 

 excellent, permanent, plastic mounting mediums on the market. Canada bal- 

 sam and glycerine jelly eventually deteriorate. Keep in mind that KOH or 

 lye will burn flesh and eat holes in clothing. 



Pelecypod Features 



Shape of shell. In most families of bivalves, the shape of the shell is 

 extremely important as a species character, and only in a few groups, such 

 as the oysters and mussels, is shape so variable within a species as to be of 

 little taxonomic value. Shape of shell, as a whole, is of little value in deter- 

 mining families or genera, except in a few instances such as Pecten, Spon- 

 dylus and Pinna. 



Parts of the shell. The two valves of a clam are bound together by a 

 brown, chitinous ligament, and usually hooked together by a hinge which is 

 furnished with interlocking teeth. The valves are kept closed by powerful, 

 internal adductor muscles but kept spread open by the action of the liga- 

 ment when the animal relaxes or after it is dead. Each valve is a shallow, 

 hollov/ cone, with the apex, from which point growth of the valves com- 

 mences, turned to one side. This apex is termed the umbo (plural: umbos, 

 umbones) or beak. The hinge and its teeth are usually just below the beak 

 on the inside of the valve. The prodissoconch is the embryonic shell of the 

 bivalve, and corresponds to the protoconch or nucleus of the gastropods. It 

 is generally eroded away in adults, but when preserved it serves as a useful 

 identification character, especially in such groups as the oysters. 



Right and left valves. It is important to distinguish one valve from the 



