314 



THE AMERIC. 



rRALIST 



[Vol. LI 



adaptations on the part of two divergent associations derived 

 from some older and common source, possibly of Mississippian 

 age and of wide distribution; and it further appears probable 

 that the American Lower Coal Measures fauna is somewhat the 

 older of the two. 



The chapter on the morphology of the Coal Measures Am- 

 phibia contains a careful description of the characters of the 

 skull and other parts of the skeleton, but the author is extremely 

 chary of generalizations. He might have mentioned, for in- 

 stance, the interesting fact that the skull-pattern of these am- 

 phibians is a shifting mosaic, one in which several of the dermal 

 elements have different contacts and different positions in the 

 various families. In some microsaurs, for example, the post- 

 orbital grows backward and secures a broad contact with the 

 tabular; in others it retains its primitive position. The jugal 

 and lacrymal also differ widely in their form and contacts. The 

 nasals and adjacent elements are small and much crowded in 

 many branchiosaurs and microsaurs, long and wide in most 

 labyrinthodonts. Certain dermal elements are present in some 

 and absent in others, especially the intertemporal and the rare 

 interfrontal and internasal elements. The shape of the occiput 

 differs widely, sometimes truncate posteriorly, with the auditory 

 notch obsolete, sometimes angulate posteriorly, retaining the 

 primitively wide auditory notch. Very curious is the tendency 

 of the different families of microsaurs to develop "horns" — 

 sharp backwardly projected apophyses in the occipital region- 

 growing sometimes from the tabular, sometimes from the squa- 

 mosal and sometimes from both at once. These remind one of 

 the backwardly directed processes from the "epiotic" and supra- 

 occipital in the skull of teleost fishes and perhaps they may have 

 served for the attachment of longitudinal ligaments or muscles 

 in wriggling, aquatic types. 



All the differences in skull pattern may be regarded as minor 

 readjustments which were taking place after the more profound 

 transformation of a generalizoil pro-gai)oi(l skull into the am- 

 phibian type, the greatest iilffrat i«»ti indiKiiiig the loss of the 



