Remarks on the Plumage of Birds. 477 



your Magazine * a description of the opercula of the Ser- 

 pula triquetra and Serpula vermicularis, which Dr. Turton 

 had named as " Patella tricornis and Patella extinctorum," 

 supposing them to be individuals of the Patella family. At 

 that time, neither Mr. Glossop nor myself had examined a 

 sufficient number of specimens to be certain to which of the 

 Serpulae each operculum belonged; for the shells are so very 

 brittle, as well as minute, that it is with great difficulty they 

 can be taken out uninjured. I have lately had an opportunity 

 of examining about 200 specimens of both species of Serpula 

 (for they are always found together) ; and I am satisfied that 

 both opercula belong indiscriminately to either Serpula. I 

 have taken them from each repeatedly. I have also ascer- 

 tained that the extinctorum and tricorne, as Turton called 

 them from their shape, are only different states of the same 

 operculum. I have sent several specimens to the Zoological 

 Society, where they can be examined ; I have also a number 

 left, which show distinctly the intermediate state between a 

 complete extinguisher, or cone, and a tricorn, or three-horned, 

 operculum. I am of opinion that the cone shape is the first 

 formed, for I have several cones with one horn, and others 

 with two upon them. The three-horned operculum is also a 

 cone ; but it would appear that, when the three horns are 

 completed, the cone is lessened in height by absorption, and 

 increased in span at the base. The accompanying diagram 

 {Jig. 58.) will explain rny description. 



58 





a, Operculum extinctorum; b, ditto with one horn : found on Serpula triquetra and Serpula 

 vermicularis. c, Operculum with two horns. d, Ditto with three horns. <', e, Opercu- 

 lum tricorne. /, Opercula of their natural size. 



Art. VI. Some Remarks on the Plumage of Birds. 

 By Edward Blyth, Esq. 



Dr. Moore states (p. 361.) of the common guillemot, that 

 " Temminck considers that the lesser guillemot is the same 

 in winter dress ; but, in that case," he adds, " it is difficult 

 to account for the occasional appearance of the bird in its 

 summer plumage at that season." Montagu speaks of one 

 shot in Devon, in January; and I have a specimen, killed 

 February 20. 1830. It may be the young, which abounds 



* See Mag. Nat. Hist., vol. viii. p. 621. — Ed. 



