Reviews — Prof. H. Credner — On Labyrinthodonts 569 



The typical Oreodonts or Ruminating Hogs, as they were not 

 inaptly termed by their original describer Prof. J. Leidy, occur in 

 the North American Miocene, from the Loup-Fork to the White 

 River beds ; but they are also represented in the Uinta or Upper 

 Eocene, while Helohyus of the Bridger or Middle Eocene should 

 perhaps be also included in the family. 



Professor Scott takes as the chief character of the family the 

 circumstance that the lower canine tooth resembles the incisors, 

 while the form and function of the canine is assumed by the first 

 lower premolar. The family is divided into three subfamilies as 

 follows, viz. : — 



I. Upper molars with five crescents — Protoreodontince. 

 II. Upper molars with four crescents. 



1. Orbits closed, a lachrymal depression, no diastema, all the 



premolars simpler than the molars — Oreodontince. 



2. Orbits open, no lachrymal depression, a diastema, the last pre- 



molar molariform — Agriochoerince. 



The Protoreodonts are the earlier and more generalized forms, and 

 the presence of five crescents on their upper molars suggests affinity 

 with the Anthracotheriida and Anoplotheriidce. It is indeed curious 

 to observe that the reduction in the number of crescents on these 

 teeth in the two more specialized subfamilies of the Oreodonts is 

 precisely paralleled among the Anthracotheroids by the specialized 

 Sivvalik genus Merycopotamus, which has only four such crescents. 



We hope that the learned author of this important memoir will 

 see his way to treating other groups of extinct American mammals 

 in the same masterly manner. R. L. 



III. — Professor H. Credner on Permian Labyrinthodonts and 



Reptiles. 



Die Stegocephalen und Saurier aus dem Rothliegenden des 

 Plauen'sohen Grundes bei Dresden. By Hermann Credner, 

 Zeitschr. deutsch. geol Ges. Vol. XLII. (1«90). Illustrated. 



IN this memoir Professor Credner continues his elaborate and 

 interesting investigations into the Labyrinthodont and Reptilian 

 fauna of the Rothliegendes of the neighbourhood of Dresden ; the 

 species treated of in the present fasciculus being, if possible, of more 

 than usual interest. 



The first section of the memoir before us is devoted to the descrip- 

 tion of the skeleton of the Labyrinthodont genus Hylonomus, from 

 which the author regards Hyloplesion of Fritsch as inseparable. The 

 members of this genus comprise minute forms common to both the 

 Old and New Worlds, the detailed anatomy of which can only be 

 worked out by those who have the abundant material and exemplary 

 patience which it appears to be the good fortune of the author to 

 possess. The plates and woodcuts with which the memoir is so 

 richly illustrated speak for themselves as to the care with which 

 these details have been worked out. One point, howevei", strikes 

 us as requiring further illustration, and the author will perhaps take 



