CRUSTACEA. 



a vegetable nature, whilst as to others (such as Nereites) no 

 certain conclusion can be arrived at. Upon the whole, it 

 would be safest to adopt Mr. Sailer's proposal, and refer all 

 these remains provisionally to the artificial genus Helminthites, 



Fig. 93. Crossopodia Scotica, an Annelide track. Silurian. (After M'Coy.J 



retaining Scolithus for the burrows. As regards the distribu- 

 tion of these remains, it is sufficient to say that they occur 

 more or less abundantly in almost all strata of a suitable 

 mineral character from the Cambrian Rocks upwards. 



CHAPTER XIV. 



ARTHROPOD A. 



CRUSTACEA. 



DIVISION ARTHROPODA, or ARTICULATA. The members of 

 this division of the sub-kingdom Annulosa are distinguished 

 from the preceding division of the Anarthropoda by the pos- 

 session of jointed appendages, articulated to the body. The body 

 is composed of a series of segments or " somites" arranged along a 

 longitudinal axis; each segment occasionally, and some always, 

 being provided, at some period of life or other, with articulated 

 appendages. Both the segmented body and the articulated limbs 



