Revieics — Prof. Credner — On Branchiosaurus. 277 



to stand ; and if P. petrolei be identical with B. gracilis, there can 

 be no question as to the right of the former specific name to 

 supersede the latter. 



Coming to the proper subject of the paper under consideration, it 

 appears that the youngest specimen which came under the author's 

 notice was about 25 mm. in length. In this stage the animal was 

 aquatic, and breathed by gills, which were supported by four pairs of 

 branchial arches. The cartilaginous dorsal segments of these arches 

 were furnished with small calcified denticules ; and the ventral 

 segment of the first was ossified. By the time, however, these 

 animals had attained a length of from 60 to 70 mm., they cast their 

 branchial arches and became air-breathers ; their development being 

 thus analogous to that obtaining among the SaJamanclridce of the 

 present day. The adults measure from 100 to 130 mm. in length. 



This metamorphosis from a water- to an air-breather was accom- 

 panied by the following changes in the structure of the skeleton. 

 The short and wide skull of the larva becomes relatively narrower ; 

 the proportion of the transverse to the longitudinal diameter being 

 2 to 3 in the larva, whereas these two diameters in the adult are 

 subequal. The relative increase in length is mainly confined to the 

 anterior cranial bones ; and the orbits, and more especially the 

 parietal foramen, do not enlarge at the same rate as the surrounding 

 bones. In the pectoral-girdle,' while the coracoid and supra-clavicle 

 only increase in size proportionately with the general growth of the 

 animal, the median element (interclavicle) of the ventral buckler, 

 which is very minute in the larva, attains a length of 8 or 9 mm. 

 and forms a pentagonal bone, interpenetrated by slits from the 

 anterior border. The lateral bones (clavicles) of the shield in the 

 larva are small and in contact with each other in the median lines ; 

 but as development advances they become relatively broader, and 

 separate. In the vertebral column it has been found that while in 

 the larva the presacral vertebra are 20 in number, they are 26 in the 

 adult, this being accompanied by a diminution in the relative length 

 of the tail in the former. This remarkable change Prof. Credner 

 explains by a gradual backward shifting of the pelvis as the animal 

 increases in age, from which it necessarily follows that the sacral 

 vertebra of the larva become lumbar in the adult. With the 

 lengthening of the presacral vertebral column the bones of the limbs 

 do not keep pace ; so that the limbs of the adults are relatively much 

 shorter than those of the larva. During the above-mentioned 

 changes the dermal and epidermal skeleton is likewise undergoing 

 evolution ; and in the adult the ventral surface of the body is 

 protected by a complete and complex covering of dermal scutes, of 

 which the author has succeeded in tracing out the arrangement; 

 while in the young larva this covering is totally wanting. 



Prof. Credner is indeed to be congratulated on having traced in 



1 Prof. Credner employs a nomenclature of ftie elements of the shoulder-girdle 

 different from that adopted by many writers ; hut the equivalent terms are noticed 

 on p. 607 of his memoir. In this notice we employ the terms used in the " British 

 Association Eeport ' ' on the Labyrinthodontia. 



