FAMILY VERMETID^. 



Shell tubular, septate within, attached or free; sometimes 

 regularly spiral when young, always becoming irregular in the 

 adult growth ; aperture rounded, usually entire, sometimes fis- 

 sured. Operculum corneous, annular, sometimes spiral, rarely 

 absent. 



Animal vermiform, elongated, with short snout and distant 

 short tentacles, bearing eyes at their outer bases ; foot small ; a 

 single elongated branchia, no copulatory organ ; two corneous 

 jaws; dentition (PL 30, fig. 9). 



These aberrant mollusks were separated by Cuvier in 1830, as 

 an order under the name of Tubuli branch iata, corresponding 

 with Tubispira, Desh., 1830, and Protopoda, Gray, 1837. A more 

 extensive acquaintance with the modifications of the breathing 

 organs in mollusks has tended to diminish the importance which 

 Cuvier attached to them. 



These animals, generally attached upon shells, or coral, or 

 living in sponges, often gregarious in large colonies, although 

 without copulatory organs are unisexual, oviparous or viviparous. 

 The egs are often attached to the tube itself. The embryos 

 (PI. 48, fig. 6) are furnished with a spiral shell and the young are 

 often perforating. 



Like most attached shells the Yermetids are exceedingly irreg- 

 ular in growth, sculpture and coloring, often reproducing the 

 surface upon which they are fixed. The species are therefore 

 very difficult to identify satisfactorily, particularly as in many 

 specinens the parts wherein reside the characteristic marks, the 

 mouth , the operculum , etc., are wanting. The difficulty is enhanced 

 by the great resemblance of some of the forms to annelids of the 

 genus Serpula from which they may be distinguished by the 

 spiral nuclear shell, and interior septa of the tube. The tube 

 of Serpula is composed of two calcareous la}'ers, that of Ver- 

 metidse of three. As to the lamellae occurring within the tube, 

 on the columellar or parietal wall, they are often wanting, perhaps 



(163) 



