H. L. Moodie — Ancedors of the Reptilia. 217 



phyllosi)OiicIylous r ribs long and curved, always intercentral ; usually 

 single-headed, although there is at times an enlargement as though an 

 incipient bicipital condition were present ; sacral ribs single ; dorsal 

 vertebral series variable ; tail sometimes containing over seventy-five 

 vertebrae, the distal ones composed of the two pleurocentra ; pectoral 

 girdle invariably, in the American forms, composed of interclavicle, 

 clavicles, and scapulae. There is no evidence of a cleithrum in the 

 forms from North America; pelvic girdle composed of an osseous 

 ilium and ischium, pubis cartilaginous, sometimes calcified ; articular 

 surfaces of the limb bones well formed ; carpus and tarsus carti- 

 laginous ; digits four in the hand and five in the foot ; phalangeal 

 formula 2-2-3-2 and 2-2-3-4-3 ; abdomen usually covered with an 

 armature of scales, scutes, or rods ; overlapping or rounded scales 

 sometimes present over the entire body ; skull stegocrotaphous with 

 pineal foramen invariably present; supra-occipital plate and epiotics 

 well developed. The palate so far as known has the pterj'goids 

 approximate, but the evidence is unsatisfactory. Onlj- a fractured 

 portion of a skull presents the palate for study. According to Jaekel 

 the pterygoids are separated by the parasphenoid. It is unfortunate 

 that more is not known of the palate, but the skulls are almost always 

 preserved on their ventral surface, and only by preparation such as 

 Jaekel has employed is it possible to obtain satisfaction as to the 

 palatal condition. Material is not yet sufficiently abundant to admit 

 of this. 



In size the Microsauria show a wide range of structure. The 

 known forms range from the minute Odonterpeton trianciularis, 

 Moodie, with a skull only 6^ millimetres in length, to Macrerpeton 

 huxleiji, Cope, or Eosmirus acadtanus, Marsh, which undoubtedly 

 attained a length of many feet. The skull bones may be smooth 

 or sculptured. The ribs may be long and slender or short and 

 thick, but always curved. The limbs may be powerful or weak. 

 If the Aistopoda are degenerate Microsaurians, as appears probable, 

 the limbs may be entirely absent. The tail may be very short 

 or very long with the vertebrae laterally flattened, .proving the 

 aquatic habit of the animal. The ungual phalanges are either 

 sharp or blunt. The form is undoubtedly lizard-like, as is proven 

 by the impressions of the bodies. The neck is very short, the 

 pectoral girdle being closely attached to the head, but I have never 

 seen an indication of the piscian union of pectoral girdle and skull. 

 The body may be long and slender or short and thick. In short, 

 there are a great variety of shapes and forms associated with 

 a multitude of anatomical structures, which give a vast range of 

 possibilities for development. The group is widely heterogeneous. 



The differences between the earliest known reptiles and the 

 Microsauria, so far as known, are the possession by the reptiles of 

 osseous carpus and tarsus and the two sacral vertebrae associated 

 with a more highly developed condition of the limb bones. These 

 differences are not at all insurmountable. Unfortunately the skulls 

 of neither of the two best preserved Carboniferous reptiles, laodecfes 

 copei, Williston, and Saiiramis costei, Thevenin, are preserved. They 

 were undoubtedly stegocrotaphous. It would be of the greatest 



