510 



This is to be met with from the fize of afewinfthread 

 to that of a fwan's quill, as frequently in groops, twifled 

 and contorted in all direfiions, as fingle; and is never 

 obferved to fpread at the bafe, or to pofTefs the fmallefc 

 degree of carina along the back ; and is generally at- 

 tached its whole length to fome other body : this cir- 

 cumflance, independent of the difference in the animals, 

 is the only leading charafter, by which it mav be known 

 from S. tubularia, which is attached only in part to- 

 wards the fmaller end, and ufually afcends in a confide- 

 rable an^le. 



o 



We have feen both thefe (hells mod complicatedly 

 entwined with each other, and mixed with S. triquetra ; 

 and fome of the laft pofTefling fo little appearance of a 

 ridsje along the back, that had not the animals been 

 confulted, it would not have been pofTible to have di- 

 vided them. As the animals therefore are the only cer- 

 tain criteria, thefe (liells, as well as many others of this 

 intricate genus, will ever be confounded in cabinets. 



It may be thought, that although we have brought 

 four of the Linncean fpecies into two, in fome inftances 

 we have multiplied others of the Brif?//iSerpulce : to this 

 it can only be faid, that as far as human fallibility will 

 admit, care has been taken to fix chara6iers of diftinfli- 

 on, from fhape, habits, or animal ; except, therefore, 

 in 5. reverfa, we have not a doubt but thofe defcribed, 

 are really diflinti. The inhabitant of that (hell, we muft 



conlefs. 



