34 THE COAL MEASURES AMPHIBIA OF NORTH AMERICA. 



larity between the arrangement of the lateral-line systems on the tail of Necturus, 

 Micrerpetou, and Eumicrerpeton is doubtless of genetic (459) importance, indicating 

 the origin of the caudate Amphibia from the Branchiosauria by a degenerative or 

 recessive evolution in other structural characters. This system of sense-organs has 

 been described in no other branchiosaurian. 



The Microsauria (458) are exceedingly interesting in possessing a very peculiar 

 type of lateral-line system. It is known in a few forms and in one specimen espe- 

 cially well (Erpetosaitms tabulatus} (fig. 22, G). In this species, which is represented 

 by a single imperfect skull, there are evidences of a nearly complete lateral-line sys- 

 tem of canals and pits. The occipital cross-commissure is represented on the pos- 

 terior border of the skull by a row of elongate pits such as Andrews described for 

 Ceratcrpcton (8). I fail to find in American species the pores described by Andrews. 

 The temporal canal forms with the jugal canal a complete ring, much as it is in Tre- 

 matosaurus, only in Erpctosaurus tabulatus the temporal canal does not touch the 

 tabularc. I think there are indications of a connection of the temporal canal with 

 the supraorbital. The temporal canal cuts the supratemporal, the squamosal, and 

 jugal. The jugal canal lies for the most part on the supratemporal and quadrato- 

 jugal, and joins the infraorbital on the jugal. A portion only of the infraorbital 

 canal is preserved. There is also a portion of the supraorbital canal. It seems not 

 to be connected with the temporal canal, although there is a possible indication of 

 this connection. The supraorbital crosses the frontal, prefrontal, and a part of the 

 nasal. The squamosal element is peculiar in Erpctosaurus tabulatus in that it is 

 excluded from the parietal by the extension of the tabulare and postorbital. This 

 condition is found in several other species of the Microsauria. It will be noticed 

 that with the changed condition of the squamosal the temporal canal has changed 

 also, and this is further proof of the close connection between the cranial elements 

 and the lateral-line canals, as Allis has maintained for Amia. (See in this connection 

 C. J. Herrick, Journ. Comp. Neurol., vol. n, p. 224, 1901.) 



The Diplocaulia, an amphibian order allied to the Branchiosauria (477) and 

 through them to the Caudata, have the lateral-line system apparently well-devel- 

 oped. The skulls are always crushed flat, so that the canals are nearly obliterated. 

 On the mandible, however, the canals are clearly distinct and apparently run the 

 entire course around the mandibular rami. On a well-preserved skull of Diplocaulus 

 magnicornis Cope there are indications of three lateral-line canals (477, pi. i). The 

 infraorbital is clearly marked as a well-defined groove just below the orbit. The 

 supraorbital is indicated only for a short distance, and there are indications of the 

 temporal canal. The operculo-mandibular canal has its course, for the most part, 

 near the middle of the rami, but as it approaches the posterior angle of the mandible 

 it suddenly changes its course and drops down to the lower edge, only to rise again 

 and to come out strongly marked near the median plane on the posterior angle of 

 the mandible. 



The Temnospondylia, as represented by Eryops, Cricotus, and Arcliegosaurus, 

 possess well-developed lateral-line canals (458). H. von Meyer (428) many years 

 ago made out the course of the canals in Arcliegosaurus. The greater part of the fol- 



