TEREBELLA. 211 
In as far as I have observed, the generic character may be found in 
a vermicular annulate body, with pencils issuing from a number (perhaps 
sixteen) of the upper segments ; numerous extensile, flexible tentacula ; 
external ramified branchiz on the back of the neck ; the construction of 
a tube, open at both extremities, so wide as to admit reversal of the 
animal within. Specific distinction may be found in the configuration 
of the branchixw, and in the quality of the materials for binding the 
tube. 
