STEGOCEPHALIA. 131 



Hyloplesion and Microbrachis from the Lower Permian of 

 Bohemia). 



The first fragmentary remains of the Microsauria were 

 discovered in the interior of decayed tree-stumps in the Coal 

 Measures of South Joggins, Nova Scotia; but the only satis- 

 factorily-preserved skeletons hitherto obtained, are from the 

 Lower Permian of Saxony and Bohemia. 



Hyloplesion (figs. 83 3, 4, 5, 84 D). A small animal, rarely if ever 

 exceeding a decimetre in length, and with very slightly ossified skeleton. 

 The orbits are situated in the anterior half of the skull, and there is a ring 

 of sclerotic plates. The outer cranial bones are smooth or delicately 

 punctate ; and some bones of the palate exhibit a cluster of very minute 

 teeth. The presacral vertebrae (fig. 83 3, 4, c) are all longer than deep and 

 about 20 in number, while the caudal vertebrae seem to have been nearly 

 if not quite as numerous. All except the hinder caudal vertebrae bear 

 ribs, and these exhibit a distinct capitulum and tuberculum throughout 

 the thoracic region. Two or three pairs of cervical ribs and about three 

 pairs of lumbar ribs are comparatively short and single-headed, as are 

 also those of the anterior caudal region ; the single pair of sacral ribs is 

 much thickened as usual. The interclavicle (fig. 84 D) is T-shaped, with a 

 somewhat expanded head ; the clavicle is slender and much arched. Both 

 scapula and coracoid are ossified. A mosaic of calcified granules (.) in the 

 region of the clavicular elements may indicate a beginning of ossification 

 in the sternal cartilage. The humerus is expanded a little at each end, 

 and the direction of compression at one extremity is almost at right-angles 

 to that at the other ; there is no epicondylar foramen. The radius and 

 ulna are about half as long as the humerus ; there are traces of ossification 

 in the carpus ; the number of digits is uncertain. The ilium is unusually 

 short and expanded proximally ; the ischium and pubis are relatively 

 small and delicate. The hind limb is about as large as the fore limb, but 

 the femur is much more robust than the humerus ; a few tarsal elements 

 are ossified, and the number of digits is unknown. The ventral armour 

 consists of overlapping oval scutes with thickened hinder margin, and 

 there seems to have been a dorsal armature. Hyloplesion longicostatum, 

 from the Lower Permian of Bohemia, and H. geinitzi, from the same 

 horizon in Saxony, are the best-known species. 



The imperfectly known Hylonomus from the Coal Measures 

 of Nova Scotia, perhaps also of Lancashire, is closely similar to 

 Hyloplesion and may be generically identical with it. The 

 allied genus Petrobates (fig. 85 D), from the Lower Permian of 

 Saxony, is remarkable for the nature of its ventral shield, which 



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