... Two humble-bees, Bombus thoracicus and B. violaceus, are found on the pampas; the first, with a primrose yellow thorax, and the extremity of the abdomen bright rufous, slightly resembles the English B. terrestris; the rarer species, which is a trifle smaller than the first, is of a uniform intense black, the body ... — The Naturalist in La Plata • W. H. Hudson