56 THE COAL MEASURES AMPHIBIA OF NORTH AMERICA. 



small dermal scales, which may have covered the entire body. In form the scales 

 are ovoid, being half as wide as long, and the markings on the 'scales partake of the 

 nature of radiating lines, much after the pattern of the sculpturing of the cranial 

 bones in the Microsauria. The scales are less than 0.5 mm. in diameter and their 

 character can only be ascertained under high magnification. Near the middle of 

 the tail there are preserved distinct transverse bands of dark color, which are more or 

 less evident throughout the entire tail impression, but they are elsewhere not so 

 distinct as in the central region. The lines are evidently due to rows of pigmented 

 scales, and in all probability the animal's body was transversely striped. 



The most interesting and important single structure discovered on the specimen 

 is the impression of the lateral-line system, which is clearly evident as two dark 

 lines on the impression of the fleshy part of the tail. The sense-organs are repre- 

 sented by two longitudinal rows of pigmented scales, one beginning at the tip of the 

 tail, the other taking its origin from the median line somewhat further forward. I 

 am indebted to Dr. Katashi Takahashi for calling my attention to the similarity of 

 this arrangement to that found in the recent Necturus. The arrangement and dispo- 

 sition of the lines containing the sense-organs is practically the same in the two 

 forms. The median lateral line takes its origin from the extreme tip of the tail and 

 is continued to the base, where the impression is broken. The dorsal lateral line 

 has its origin rather abruptly from the median lateral line at a distance of 6 mm. from 

 the tip of the tail. The sense-organs were undoubtedly located beneath specialized 

 pigmented scales on the surface, and to this pigment is due the preservation of 

 the lines. 



The fact that the arrangement of the sense-organs of Micrerpeton corresponds so 

 exactly to the condition found in Necturus is of considerable interest. Necturus 

 alone among the modern tailed Amphibia has the arrangement described for the 

 lateral-line system of Micrerpeton. All other forms of the Caudata, as also the larval 

 forms of the Salientia, have an arrangement of the lateral-line system which is per- 

 fectly distinct from that found in Necturus, although the basis of the same arrange- 

 ment is found in all. In Amblystoma, for instance, the median lateral line is not 

 present on the tail, and the dorsal line is incompletely developed. The close simi- 

 larity of the arrangement of the systems of sense-organs in the two forms, Micrer- 

 peton and Necturus, may be of genetic significance with regard to the latter form. 

 The lateral-line sense-organs are of a very fundamental significance, and it is not at 

 all improbable that the same arrangement of the lines has existed from the Carbo- 

 niferous period or earlier. We know that such has been the case in a great many of 

 the fishes. The ancestors of the modern Caudata must have originated somewhere 

 in the basal Carboniferous or earlier periods, and, in the writer's opinion, the Branch- 

 iosauria represent the ancestral group of the Caudata. This suggestion is by no 

 means new, since Baur and others have held the same view. This topic has been 

 discussed at length elsewhere (459) by the writer. 



The relations of the form Micrerpeton caudatitm are readily determined. The 

 number of the presacral vertebra?, the form and position of the ribs, the shape of the 

 skull, the arrangement of the cranial elements, the structure of the pectoral girdle 



