On the Reproduction of a lost part of an Operculum, 419 



XXXVIII. — On the Reproduction of a lost part of an Operculum, 

 and of its probable Restoration when entirely destroyed. By 

 Dr. J. E. Gray, F.R.S., V.P.Z.S. &c. 



It is to be expected that an operculum of a Gasteropodous Mol- 

 lusk might be sometimes broken or injured, but I have never 

 been able to find any very distinct example of the kind, so as to 

 study how the repair of the lost part would be effected. That 

 such an occurrence would most probably be rare, is easily ex- 

 plained from its situation, as the operculum is protected by the 

 last whorl of the spire of the shell when the animal is expanded, 

 and by the mouth when it is contracted into the cavity of the shell. 



I have lately met with a very distinct example in a spe- 

 cimen oi Fusus in the British Museum collection. Yis. 1. 

 In this specimen the apical half of the operculum 

 has been broken off (see fig. 1), and the lost part 

 has been renewed by an irregular roundish pro- 

 cess, nearly of the size of the lost part, not quite 

 as thick as the original portion, and formed of 

 rather irregular horny plates ; the smaller or first- 

 formed portion being in the centre of the broken 

 line, so that the restored part bears some similarity 

 to the annular operculum of a Paludina. This restoration is 

 exactly like that which would have taken place in a shell under 

 similar circumstances, and is a further proof of the truth of the 

 theory which I have long advocated, that the operculum is a ru- 

 dimentary valve, and is homologous to the second valve of the 

 Bivalve Mollusks. 



In examining two specimens of Pleurotoma babylonica, pre- 

 served in spirits, with the opercula attached, I was much sur- 

 prised to observe that the opercula of the two specimens were 

 exceedingly different in structure and belonged to two distinct 

 modifications of that valve, one (fig. 2) being subannular, with 

 the nucleus apical, like the other species of the genus, and the 

 other (fig. 3) annular, with the nucleus subcentral, somewhat 

 like the operculum of Paludina. 



Fig. 2. 



Fig. 3. 



The examination of the restoration of the lost half of the 



27* 



