302 POLYCHAETA chap, xi 



acicula and the hard jaws are preserved in certain rocks, ; and 

 can be referred to existing families. Eunicites avitus l is repre- 

 sented by a double series of acicula, indicating the parapodia of 

 the two sides ; and by remains of both upper and lower jaws (Fig. 

 159). Four different species of the worm have been described 

 from the lithographic slate of Bavaria, of Jurassic age ; and 

 several upper jaws of other Eunicids have been discovered in 

 the Palaeozoic beds of Canada and Scotland, and have received 

 the names Lurtibriconereites, Oenonites, and Arabellites, in reference 

 to their nearest allies amongst living genera. 



There are, however, numerous remains, in the forms of tracks 

 or casts, in the earlier rocks, which have been referred to the 

 Polychaeta. The names Crossopodia, Myrianites, Nereites, Phyllo- 

 docites, have been given to some of these traces, though they are 

 open to numerous other interpretations. Some of the " tracks " 

 are similar to those made by living Crustacea in walking 

 over wet sand ; others appear to be the casts of some animals. 

 Tubular burrows in rocks or fossils, some straight, others 

 U-shaped, have received such names as Arenicolites, Scolitlms, 

 Histioderma ; whilst under the name Lumbricaria certain cylin- 

 drical, coiled structures, resembling worm "castings," are met 

 with in this same lithographic stone of Solenhofen. Many of the 

 tubes referred to Polychaetes by the earlier palaeontologists have 

 been transferred to other groups : thus Cornulites is now believed 

 to be a Pteropod shell. 



This very meagre geological record is quite insufficient to 

 form any basis for a phylogeny of the group. And this 

 poor supply of remains is not surprising, when we consider the 

 soft nature of the tissues, the absence, in the majority of families, 

 of skeleton and of other parts which could have been fossilised ; 

 yet we might have expected a greater abundance of fossilised 

 jaws than is represented at present. But it must be borne in 

 mind that the conditions of life of these soft-bodied animals are 

 not conducive to their leaving abundant fossilised remains. 

 1 Elilers, Zeitschr. f. wiss. Zool. xviii. 1868, p. 241. 



