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 

 Serpula? 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 my description. 



58 



f 



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

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

 lum tricorne. /, Opercula of their natural size. 



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

 By Edward Bl^th, 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. 



