ANNULOSA: ANNELIDA. 



197 



elongated, and consists of a great number of similar segments, 

 with rudimentary branchias. The head is distinct, and carries 

 eyes and Teelers, whilst the mouth is furnished with a large 

 proboscis, and often with two homy jaws (fig. 59). In the 

 Eunicea the branchiae are usually well developed and of large 

 size, and the mouth is armed with seven, eight, or nine horny 

 jaws. Eunice gigantea attains sometimes a length of over four 

 feet, and may consist of more than four hundred rings. 



Distribution of Annelida in Time. — Of the Annelida the 

 only orders which are known to have left any traces of their 

 existence in past time are the Tubicola and the Errantia; of 

 which the former are known by their investing tubes, whilst 



Fig. 60. — Errant Ajinelides. A. Hairy-bait {Nephikys); E. Sea-mouse {A^krodiie)', 

 C. Lob-worm (^ rf«2C(7/rt). (After Gosse.) 



the latter are only recognised by the tracks which they left 

 upon ancient sea-bottoms, or by their burrows in sand or mud. 

 These tracks and burrows of Annelides are found commonly in 

 rocks of almost all ages from the Cambrian period upwards. 

 Those tracks which have been caused simply by the passage 

 of the worm over the surface of the mud are termed by Mr 

 Salter Helminthites, whilst the burrows are called Scolites (or 

 Scolithtis). 



Tubicolar Annelides are known to occur from the Silurian 

 Rocks upwards. The well-known Silurian fossil, Tentaculites, 

 is generally believed to belong to this order, but it is referred 

 by M. Barrande to the Pteropoda (Molhiscd). Comulites and 



