Sentence:  The letter proceeds to state that, besides this monster, there is a great variety of remains of another new order of animals, which Mr. Bain has deginated as <WSD>"bidentals</WSD>", from their possessing only two teeth, or rather tusks, in the upper jaw, and none whatever in the lower jaw. 
Meaning of the word marked with <WSD> tags:  An organism that has only two teeth, especially a dinosaur of the infraorder (noshow=1).