CHAPTER XII. 



SUBCLASS LEPOSPONDYL1A Z1TTEL, 1887. COAL MEASURES TO PERMIAN. 



(Europe and North America.) 



The group is here defined according to the English edition of Zittel's Text Book 

 of Paleontology, 1902, p. 125. "Notochord persistent and enclosed in constricted 

 bony cylinders, hour-glass-shaped in longitudinal section. Teeth simple, conical, 

 hollow. " According to Zittel there are two families, the Microsauridae and the Ais- 

 topodidae. The latter family is dealt with under Aistopoda (p. 76) and it is there 

 shown that the group is in no wise a valid one. The former family is regarded as an 

 order and is fully entitled to that rank. As defined here the subclass Lepospondv/iti 

 contains but a single order, the Microsuitria. 



Extinct, terrestrial, aquatic, or semi-aquatic amphibians; skull pitted and 

 grooved by lateral-line canals and by sculpturing marks, or the skull may be smooth ; 

 teeth present on most of the palate bones; exoccipitals cartilaginous or calcified, 

 never completely osseous; sclerotic plates sometimes present ; skull of various shapes. 

 Vertebrae with notochord largely persistent, hour-glass-shaped; neural spines low or 

 high, or absent; ribs interccntral and single-headed, with an incipient tubercle in 

 some forms; vertebral corumn differentiated into dorsal and caudal series; cervical 

 series not clearly defined. Limb bones with well-ossified perichondrium, endochon- 

 drium partly ossified; epiphyses absent; carpus and tarsus (tarsus osseous in two 

 species) cartilaginous; phalanges clawed or not; digits 4 in hand and 5 in foot. 

 Pubis sometimes calcified but never osseous. 



DEFINITION OF THE ORDER MICROSAURIA DAWSON, 1863. COAL MEASURES 



AND PERMIAN. 



(Europe and North America.) 



Lizard-like, sometimes longicaudate, stegocephalous, lepospondylous, ambu- 

 latory or legless amphibians; skull bones usually sculptured with pits and grooves; 

 lateral-line canals well developed on skull bones; skull with horns from tabulare 

 and supratemporals or without horns; branchiae never persistent; sclerotic plates 

 present ; orbits usually well forward. Vertebrae hour-glass-shaped ; endochondral 

 bone weakly developed throughout skeleton, especially in vertebras; notochord 

 largely persistent; neural spines low and rudimentary or long, fan-shaped, and 

 highly ornamented. Dorsal series of vertebral column variable; usually from 22 

 to 30; tail containing sometimes over 75 vertebrae, or tail very short with 2 weakly 

 developed vertebrae; caudal ribs present, in those forms with long caudal series 

 the distal vertebras sometimes exhibiting 2 pleurocentra. Ribs long and curved, 

 always intercentral in position, single-headed, with at times an incipient tubercle. 

 Pectoral girdle composed of scapulas, clavicles, coracoids, and interclavicle. 

 Pelvic girdle composed of osseous rod-like ilium, plate-like ischium ; pubis carti- 

 laginous, sometimes calcined. Limbs present or wanting or weakly developed, 

 sometimes present in front and wanting behind. Radius and ulna and tibia and 

 fibula free; carpus and tarsus usually cartilaginous ; digits 4 in hand and 5 in foot, 

 terminal phalanges sometimes clawed. Phalangeal formula for the hand 2-2-3-2, 

 for the foot 2-2-3-4-3. Abdomen covered with dermal armature composed of 

 osseous or corneous rods or scutes ; overlapping scales, fish-like in appearance, some- 

 times present over the entire body ; body also covered with lizard-like scales or naked. 



75 



