390 Miscellaneous. 



Linnaeus made two species of this Planorbis, it is clear, from the 

 openin°- lines of the paragraph, that the sense intended to be con- 

 veyed is not that which he has presented. They are as follows : — 



" The minute, semitransparent, homy shell of this species, more 

 generally known to collectors by the second name which Linnaeus 

 gave to it, &c." I am, Gentlemen, 



Your obedient Servant, 



Lovell Reeve. 



With reference to the foregoing letter, we may remark — 



1 st. That what Mr. Reeve says respecting the tenth edition of the 

 « System a Naturae ' is totally at variance with the generally received 

 opinion of naturalists that the twelfth is the standard edition of 

 Linnaeus' s work, which is to be referred to and followed. 



2ndly. That we are fully aware how greatly Mr. Reeve is indebted 

 to the work of M. Moquin-Tandon, and regret that he has so im- 

 plicitly followed that author in numerous erroneous changes in 

 nomenclature. 



3rdly. That Mr. Reeve, however, must not shift the adoption of 

 the name Planorbis crista on to his favourite authfir's shoulders. 

 Among Mr. Reeve's own synonymy of the species, we find "Planorbis 

 (Gyraulis) nautileus, Moquin-Tandon (1855), Hist. Moll. vol. ii.p.438, 

 which is utterly irreconcileable with the statement in his letter that 

 he follows that author in the adoption of the name Planorbis crista. 



4thly. That only one construction can be put upon the following 

 passage in his work : — "It may be observed that Linnaeus and Dra- 

 parnaud both made two species of this. The names crista and cris- 

 tata have been given to young specimens, and nautileus and imbri- 

 catus to adult specimens." What can this mean, but that, just as 

 Draparnaud made two species of the shell which he called cristatus 

 and imbricatus, so Linnaeus made two species which he called crista 

 and nautileus ?— a statement at variance with the facts. 



On the true Nature of Pleurodyctium problematicum. 

 By Carl Rominger, M.D. 



Under the above name I have long kept in my cabinet a specimen 

 collected at Kirchweiler, in the Eifel Mountains. After having 

 identified it with the fossil described by Goldfuss, I laid it aside ; 

 and only recently, twenty years afterwards, when I happened to look 

 over it again, the first glance convinced me that the Pleurodyctium 

 problematicum is merely the cap of a Fuvosites, or, more accurately 

 speaking, of a Michelinia. I have subsequently found that Milne- 

 Edwards had already recognized the family affinity between Favosites 

 and Pleurodyctium, without, however, suggesting a generic identity 

 of the two. 



The fossil from Kirchweiler is represented by a lenticular cavity, 

 a little over one inch in diameter and scarcely half an inch deep. 

 To one side of this cavity are attached the bases of conical sub- 



