DR. W. BAIRD ON KEW TUBICOLOUS ANNELIDES. 11 



species which eau be determined, it is my intention, from time to 

 time, to offer to the Linnean Society, if approved of, descriptions 

 of such species as appear to me new or worthy of particular 

 attention. 



Family SEEPULID^. 



The genus Serpula of Linnaeus, as established by the illustrious 

 Swede, contained several species now known to belong to the 

 genus Vermetus, a genus of moUusks. After these were with- 

 drawn, there still remained many forms of shelly tubes which, 

 though bearing a general resemblance to each other, were difl&cult 

 to be arranged under one single genus. The animals, however, 

 the architects of these tubes, after a time began to be a little 

 more studied ; and thus Lamarck, Blainville, Savigny, and some 

 other naturalists were enabled to construct, upon good grounds, 

 several genera to contain what might otherwise have been con- 

 sidered similar forms. The last author who has paid particidar 

 attention to this Linnean genus is Dr. A. Philippi. His sub- 

 divisions of Serpula are founded upon a character which has been 

 discovered by malacologists to be of great value in the class Mol- 

 lusca. The animals of the greater number of the species of 

 Serpula which have been described possess a similar organ to that 

 which characterizes so many of the G-asteropodous MoUusca. 

 This is the operculum, which varies considerably in structure in 

 the different species, and which thus forms an excellent character 

 for dividing them into genera. As Philippi justly observes, " this 

 character has, moreover, the advantage that it may still be fre- 

 quently observed in dried specimens preserved in museums." 



Little dependence can be placed on the sTielly tuhe alone in 

 distinguishing the species or even the genera : thus we find a 

 similar shell possessed by two or three different Annelides be- 

 longing to two or three distinct genera ; for, as Philippi remarks 

 in his paper*, " the shells of Serpula triqiietra, Vermilia triquetra, 

 and Pomafoceros tricuspis are difficult to distinguish without the 

 animals." 



The structure of the operculum is far more varied, indeed, than 

 it had been hitherto supposed to be ; and I think Dr. Philippi has 

 done good service to the students of this group of Annelides by 

 so carefully distinguishing the structure of this appendage. It is 

 owing to the fact mentioned above (that the operculum frequently 



* Wiegmann's Archiv for 1844, Band i. p. 186. Translated into English by 

 Dr. Francis, in Ann. & Mag. of Nat. Hist. 1844, vol. xiv. p. 153-162. 



