pachycardia

from The Century Dictionary.

• noun A genus of prionodesmaceous pelecypods with oblong trigonal shells having terminal beaks, two strong divergent cardinal teeth, and a long posterior lateral tooth in each valve. It occurs in the Alpine Trias.
• Those vertebrates which have a thick muscular heart divided into auricular and ventricular parts, and a well-defined skull: opposed to Leptocardii. This primary group of Vertebrata contains all except the lancelets, and is conterminous with Craniota.