ALCA, in ornithology, a genus of the order of anseres. The beak of this genus is without teeth, short, convex, compressed, and frequently furrowed transversely; the inferior mandible is gibbous near the base; the feet have generally three toes. The species of the alca are six. 1. The tordo, or razor-bill, with four furrows on the bill, and a white line on each side running from the bill to the eyes. Great numbers of them hatch together in the caverns of rocks, and lay but one egg at a time. 2. The impennis, or northern penguin, with a compressed bill furrowed on each side, and an oval spot on each side of the eyes. 3. The arctica, or puffin, with a compressed bill and four furrows; the orbit of the eyes and temples are white. 4. The lomvia, or seahen, with a smooth oblong bill, and the upper mandible yellow on the edges. 5. The grylle, or Greenland dove, with a smooth subulated bill, and a large white spot on the belly and wings; the feet are red. 6. The alle, or black and white diver, with a smooth conical bill, a white streak on the belly and wings, and black feet. All the species of this genus frequent the northern shores of Europe.