Quast 1948 Journal 80 May 24 Las Cuevas, 23°34'N, 109°39'W, Baja California tightly packed, chittering bats. The tightly packed bats were clustered on almost vertical side walls and were determined to be Myotis velifer while many Natalus mexicanus were hanging nearby, mostly in the small hollows opening downward from the rock. One Natalus mexicanus was seen hanging among the Myotis velifer that blanketed some spots of the cavern walls, but some of the hollows in the rocks contained equal quantities of Myotis and Natalus, crowded together. Some of the openings of the hollows were so small that the tightly packed bats had to be stirred out with a stick. Several Macrotus californicus were seen hanging in the highest parts of the cave (about 25 feet). There was casily a thousand Myotis velifer within the medium-sized cave with perhaps two-hundred or less Natalus mexicanus. My estimate on the number of Myotis is conservative in comparison to some of the other ones. One part of the floor was covered with a mass about 3 feet square of small black beetles. As the bats began flying, the chittering increased and we started raining down on our heads. 53 Natalus mexicanus were netted and saved and 28 Myotis velifer. The second cave was very spectacular because of its large size. Its opening was about 80 ft.