10 



SERPULA. 



A. Flexuous, irregular, and adhering. (Plate 



XXII. Fig. 2.) 



B. Assuming a certain form, detached. (Fig. 3.) 



Shell univalve, tubular, gradually tapering, often 

 interrupted by imperforate partitions at irregular 

 distances. Frequently closed at one end. 



By constituting two divisions of this genus, and 

 omitting the character of adherence in the generic 

 description of Linnaeus, we legally include a great 

 variety of shells, which, without this alteration, 

 were inconsistent with the definition. Many spe- 

 cies which should rank in the first division have a 

 great appearance of regularity in their structure, 

 and yet, strictly speaking, are irregular. The end 

 is twisted, sometimes the whole shell, into a spiral 

 form, much in the same manner in all the indivi- 

 duals of the species ; but there is no fixed number 

 of circumvolutions, nor any symptom of the animal 

 being directed by an invariable law, as in turbi- 

 nated and other genera. 



