_Fritschia curtidentata_ Dawson. Above: Bones of skull and anterior extremity, and bony rods of belly. Below: Bones of pelvis and posterior extremity. Nearly natural size. Erect tree, Coal formation, South Joggins, Nova Scotia. Photograph by Dawson, published through the courtesy of Dr. Arthur Willey. Original specimen in the Peter Redpath Museum of McGill University.] If now we take up a consideration of each of the characters mentioned by Lydekker we find that the first one holds good for all examples of the group. The second character, "without limbs," is not good. Species of _Œstocephalus_, _Ptyonius_, _Molgophis_ all possess limbs; and doubtless Ophiderpeton will be found to possess limbs also, since it has a well-developed pectoral girdle. The limbs in all of these genera are small. The third character, "apparently without pectoral and pelvic girdles," is not at all a good character, since nearly every specimen of some species and almost all species show evidences of pectoral girdles and a few exhibit pelvic girdles. The fourth character, "vertebræ with elongated centra and aborted neural spines," is not a good distinguishing character, since _Amphibamus_, an undoubted microsaurian, possesses the same vertebral characters. "Ribs slender, and barbed like those of fishes" is a character which is common to several widely distinct genera. All Microsauria possess long, slender ribs, and the barbed condition is one which is possessed by only a few, _Thyrsidium_, _Ophiderpeton_, etc., the so-called "barb" being merely a highly exaggerated tuberculum. The teeth of nearly all Microsauria are smooth, so that the character "teeth smooth" is not a good one for a group definition. It has not been possible to examine any of the American specimens for the plication of the dentine, since the forms are so rare and the fossils very fragile. The last character, "external gills probably persistent," is certainly not true for the American species, and the evidence for the European species is negative. Fritsch described and figured (Fauna der Gaskohle, Bd. I, 1883, p. 114, Tafeln 18 and 23) structures which he regarded as supporting structures for the external branchiæ. He says in regard to these structures: "Bei dem Umstande, dass sie von der Kiemengegend aus sich büschelförmig verbreiten und man ihren Contakt mit einer Art von Branchiæ constatiren kann, zweifle ich nicht daran, dass diese Stäbchen dem Kiemenapparate angehören. Bedenklich ist nur ihre grosse Zahl und das Vorkommen bis zum 16ten Wirbel und ich erwog die Möglichkeit, dass diese Stäbchen einem zarten Bauchpanzer angehören könnten. Da aber weiter im Verlaufe der ganzen Wirbelsäule nichts Aehnliches vorkömmt, so ist man gezwungen anzunehmen, dass _Dolichosoma_ sehr grosse lange Kiemenbüschel besessen haben muss."