194 Mr. J. Alder on the genus Jeffreysia. 



and Eulimella of Forbes and Hanley), stating that he can see in 

 it no deviation from the generic characters of that tribe, but 

 " only the specialties of individual animals/' and he considers that 

 " the soft parts give such decisive proofs of identity with the genus 

 us to leave no alternative." Occasion is hence taken to censure 

 those naturalists who make new genera out of species that have 

 already provided for them " suitable and characteristic generic 

 receptacles." It may therefore be necessary to examine more 

 carefully into the suitableness of Chemnitzia as a generic recep- 

 tacle for the species in question, especially as, so far from con- 

 sidering it so, I had ^Jreviously no idea that any naturalist, who 

 had examined the two, v/ould have placed it even in the same 

 family with that genus. 



With respect to the shell, Mr. Clark says, that " the reflection 

 of the apical turn alone would almost have determined him" to 

 allocate it in C/iemnitzia." I agree with Mr. Clark in the value 

 of this character in determining the geniis (or rather family) to 

 which a species belongs. But the question is, has the shell of 

 Jeffreysia this character ? According to my observations, it has 

 not : and I am supported on this point by the testimony of 

 Mr. Jeffreys, who has stated in the 'Annals' for January las<^, 

 that he has examined about a hundred specimens without finding 

 such a character in any of them . 



We now come to the operculum, which, as 1 have stated in 

 the description of the genus, is very peculiar. Mr. Clark says 

 that this species has " the usual coi-neous operculum " of Chem- 

 nitzia ; but what that gentleman considers the usual form we 

 have some diflSculty in making out from his imperfect descriptions 

 of this part. It may be as well, therefore, to state what the real 

 character of the operculum in Chemnitzia is. There are two prin- 

 cipal types of form in this part — the spiral and the annular : to 

 these may be added the unguicular, which perhaps may generally 

 be I'educed to a rudimentary or abnormal form of one of the 

 others. The operculum of Chemnitzia is formed on the spiral 

 type ; that of Jeffreijsia on the annular. These differences will 

 be better understood by giving a figure of 

 each, which I the more willingly do as the 

 operculum of Chemnitzia (or Odostomia) is 

 not figured in any British work. The spiral 



form in most of the species is incomplete, ^ „. ., , ,. . 



• .• p , ,11,., 1 ii C. Jitssotiles, J.diaphana. 



consistmg ot about halt a turn, and the nu- 

 cleus is terminal • in those species where there is a complete vo- 

 lution the nuelv'us is brought a little nearer the centre, but is 

 never central. The striae of growth run across the opercular 

 disc, and there is an impressed line down the centre *. Very 



* I have fignred the operculum of Chem. Rissnides, because Mr. Clark, 

 in describing that species, compares it to the operculum of Jeffreysia dia- 



