POLYCKLETA. 



479 



of this nature do, however, occur occasionally in finely-levigated 

 sediments, such as the Lithographic Slates (Jurassic) of Germany 

 and the Eocene Slates of Monte Bolca. Impressions of this kind 

 not only exhibit the form of the body, but may show the lateral 

 setae (fig. 344) and the jaws in place ; and upon such Ehlers 

 founded the genera Eunicites, Lumbrico?iereites, and Meringosoma^ 

 all of which were originally described from the Lithographic Slates 

 (Jurassic) of Germany. 



Apart from the comparatively very rare cases in which, as above 

 described, the body of the worm is 

 itself partially preserved, it has been 

 shown by Hinde and others that the 

 horny jaws of Annelides are by no 

 means of rare occurrence even in 

 strata as ancient as the Ordovician, 

 so that the Palaeozoic seas must 

 have been tenanted by vast numbers 

 of these animals. The jaws of An- 

 nelides (fig. 345) usually present 

 themselves as minute, dark, shining 

 objects, wholly unconnected with 

 one another, or with the remains of 

 the animal to which they originally 

 belonged. Though probably partly 

 calcified, the jaws seem to be in the 

 main composed of chitine, as they 

 are not destroyed by the action of 

 mineral acids. They average about 

 y^ inch in length, but a few reach a 

 length of a third of an inch. In 

 form, the jaws are very variable. 

 In one type (fig. 345, a), the jaw 

 is long and narrow, with a series of 

 nearly similar teeth on one margin ; 

 in another common form, the jaw is 

 furnished with a powerful anterior 

 hook, which may be immediately 

 succeeded by a series of small teeth, 

 or may have the latter on the straight 

 edge of a wide posterior extension 

 (fig. 345, b) ; other varieties are in 

 the shape of simple hooks with a 

 wide flange -like extension behind 

 (fig. 345, c) ; while others are falciform, with a series of small teeth 

 on the curved upper edge. There are other variations in the shape 



Fig. 344. — The impression of an Errant 

 Annelide (Eunicites avitus), from the 

 Lithographic Slates of Eichstadt, of the 

 natural size. (After Zittel.) 



