COl^CHYUA—DITHYRA. xxxix. 



41. Cardium. 



* costis spinosis vel tuherculatis. 

 the ribs armed with spines or tubercles. 



1. aculeatum, costis 2\ , anticis spinosis posticis tuherculatis. 



with 21 ribs, the anterior ones spinous and the 

 hinder ones tubercled. 



2. tuberculatum, costis 21, anticis tuherculatis posticis sub- 



squamosis. 



with 21 ribs, the anterior ones tubercled and the 



hinder ones somewhat scaly. 



3. echinatum, costis 18, spinis numerosis injlexis. 



with 18 ribs, armed with numerous inflected spines. 



4. elongatum, ovatum elongatum, costis 25 aculeatis. 



oval and elongated, with 25 prickly ribs. 



5. nodosum, orbiculare, costis 26 crehrd tuherculatis. 



orbicular, with 26 closely tubercled ribs. 



6. exiguum, suhtrigommi, costis 20 tuherculatis. 



somewhat triangular, with 20 tubercled ribs. 



**" costis transvcrsim squamosis. 



the ribs armed with transverse scales. 



7. edule, suhglohosum antiquatum opacum. 



somewhat globular antiquated and opake. 



8. fasciafiim, orhicvlnre depressiini suhpellucidinn. 



orbicular flat and ^^eniitraiisparent. 



■"** costis muticis. 

 the ribs unarmed. 



