But two genera and three or four species of the group are known, and of them, even, our knowledge in some respects is not as complete as one could desire. The first description of any member of the group was by the late Professor Gervais of Paris in 1867. He had only the anterior part of a single skeleton, from the Karoo beds of South Africa, to which he gave the name _Mesosaurus_, a rather meaningless term signifying “middle” or “intermediate” saurian. Nothing more was learned about any form till 1885, when the late Professor Cope described a specimen from the supposed Carboniferous of Brazil, which he believed to be closely related to _Mesosaurus_, though he had only a very imperfect specimen. He called it _Stereosternum_, also a meaningless term, since none of the animals has a “solid sternum,” nor any sternum at all, in fact! A few years later, in 1888 and 1892, the late Professor Seeley of England studied a number of specimens of _Mesosaurus_, adding not a little to our knowledge of the animals. More recently Dr. Woodward of England and Professor Osborn of America have given us still further information concerning them, and within the past few years Dr. McGregor of Columbia University has figured and described excellent specimens of a new species from Brazil, which he calls _Mesosaurus brasiliensis_. Not only were Dr. McGregor’s discoveries of great interest as settling many doubtful points in their structure, but they were still more so from the fact that he found his species so nearly like that from Africa that he placed it in the same genus. Since the proganosaurs were purely fresh-water or terrestrial animals, one can only wonder how they crossed from Africa to America, or, what is more probable, how they migrated from America to Africa, across the broad Atlantic Ocean, so long ago. The geologists tell us that the Atlantic and Pacific, in the main, have always been oceans since the beginning of terrestrial life upon the earth. Possibly the tribe of proganosaurs migrated by the very circuitous route of Europe and North America, or Asia and the Northwest; but that is very improbable, since nothing whatever resembling them has ever been found in the Northern Hemisphere, and it is quite certain that in the many thousands of years it must have taken them to travel from southern Africa to South America many of the reptiles must have perished on the way and left their remains in the rocks. The only conclusion that seems probable is that there was a direct land communication in those olden times between Africa, or at least India, and South America across what is now the Atlantic Ocean. Of course this route will be very difficult to prove, since we can never get to the bottom of the ocean to hunt for fossil proganosaurs. Were this peculiar distribution of the proganosaurs an isolated example, one might perhaps ascribe our lack of knowledge of any fossil proganosaurs in the Northern Hemisphere to the meagerness of