STEGOCEPHALIA. , 129 



Behind the sacrum the ribs are again large, but soon diminish as they are 

 traced backwards, and are wanting on the hinder caudal vertebra). The 

 interclavicle is more or less pentagonal, without a median extension 

 behind ; the relatively small and club-shaped clavicles do not meet in 

 the middle line (fig. 84*A). The scapula and coracoid are partially ossified, 

 and so are all the pectoral limb-bones except the carpus. There is no 

 clear evidence of more than four digits in the manus, and the number of 

 phalanges is apparently 2, 2, 3, 2. The ilium is very stout and hour- 

 glass shaped ; the ischium is a delicately ossified plate ; and the pubis 

 has never been seen (fig. 85 A). There are distinctly five digits in the 

 pes, and the phalangeal formula is 2, 2, 3, 4, 3. The ventral shield con- 

 sists of deeply overlapping, cycloidal scutes, each with a thickened hinder 

 free border, and the arrangement of this armour in the adult is shown 

 in fig. 82 B. The shield gradually becomes more conspicuous and extends 

 as the immature animal approaches maturity ; the skull assumes a more 

 pointed form ; the pelvic arch recedes, being originally well in advance of 

 the vertebra which develops into the sacrum ; while the limbs gradually 

 ossify and naturally become more robust. The typical species, B. 

 salamandroides, from the Lower Permian of Bohemia, attains a length 

 of about O065m. B. amblystomus, from Saxony, is larger, sometimes 

 measuring as much as 0*120 m. in length. The French specimens from 

 the Lower Permian of Autun, are commonly described under the generic 

 name of Protriton. 



Pelosaurus (figs. 81 B, 84 B, 85 B) is much like Branchio- 

 saurus, but does not appear to exhibit the supplementary 

 sclerotic plates. Melanerpeton is also an allied genus. These 

 are restricted to the Lower Permian of Saxony, Moravia and 

 Bohemia. 



Sub-Order 2. Aistopoda. 



A group of serpentiform Stegocephalia, apparently destitute 

 of limbs, occurs in the Upper Carboniferous both of western 

 Europe and Ohio, and in the Lower Permian of Bohemia, but 

 is as yet very imperfectly known. There is supposed to be a 

 tendency to fusion of the median elements of the cranial roof. 

 The vertebral centra are in the form of constricted cylinders, 

 and the neural spines have atrophied. The teeth are simple 

 cones. The comparatively slender ribs exhibit curious pro- 

 cesses, which seem to be due to the fusion of intermuscular 

 bones with them. Neither limb-bones nor traces of arches for 

 the support of the appendicular skeleton have hitherto been 

 w. 9 



