GENUS POLYSTOMELLA. 277 



Dillwyn, and many other writers of the latter part of the last and the early part of tlie present 

 century. Bv Do Montfort, indeed, tlic examples of this type that had been described and 

 figured by Fichtel and ^loll were erected into no fewer than six new genera ; neither of these, 

 however, was adopted by any succeeding systematist, until Ehrenberg (xl) revived the name 

 Geoponus long after the present designation of the genus had been fixed. Its dissimi- 

 larity to Ncuililiis \\<x% first clearly pointed out in 1822 by Lamarck, (lx) who conferred 

 upon it the generic distinction Foli/Nfo.nclla ; and his definition of the genus was as follows: — 

 " Coquille disco'ide, multiloculairc, a tours contigus, non apparens au-dehors, et rayonnee a 

 I'exterieur par des sillons ou des cotes qui traverscnt la direction des tours. Ouverture com- 

 posce de plusieurs trous diversement disposes." By Blainville this type was described (vi) 

 under the name Vorficialk ; but Lamarck's designation was restored by M. D'Orbigny (lxix), 

 who, however, altogether misconceived the structure of the organism to which it was applied. 

 The aperture, which had been but vaguely indicated by Lamarck, was described by D'Orbigny 

 (lxx) as formed by " Ouvertures nombreuses, eparses, en bordure ou formant un triangle a la 

 pmiie siiperieure de la derniere loge, et se montrant encore ouverts dans les fossettes suturales 

 des dernieres loges;" he repeated (lxxui, p. 121) the assertion that " L'animal fait sortir 

 des filamens non seulement par des ouvertures du dessus de la dernicre loge, mais encore 

 par des pores des cotes des dernieres;" and in his latest publication on the subject 

 (lxxiv) he more concisely reaffirms the same error as follows: — "Coquille nautiloi'de, 

 pourvue de nombreuses ouvertures sur la derniere loge et sur les cotes de la coquille ; 

 une cavite simple au loges :" — notwithstanding that the true structure of Poli/stomeUa criqja 

 had in the mean time been elucidated by Prof. Williamson in his admirable memoir on 

 that species (cvii). — Subsequently to Prof. Williamson's memoir, an elaborate account 

 of the characters of the genus Poli/stonicJlu, and especially of a species designated P. 

 strii/ilata (which is only one of the multiform varieties of P. crispa), has been given by 

 Prof. Max Schultze (xcvii) ; who had the advantage of being able to study this organism in 

 tiie living state, and has thus been enabled to give a beautiful figure, not merely of the 

 shell, but also of the pseudopodia protruded from various parts of its surface, as well as to 

 make preparations of the sarcode-body of the animal by dissolving away the shell in dilute 

 acid. He does not seem, however, to have had the advantage of a full knowledge of Prof. 

 Williamson's memoir, his acquaintance with it being apparently limited to the abstract of it 

 contained in 'I'lnstitut' (No. 787); and he has not availed himself as fully as is desirable of 

 the mode of examining the intimate structure of these minute objects by the preparation of 

 very thin sections. In every point, in fact, in which he differs from Prof. Williamson, I am 

 satisfied that the truth lies with the latter ; and this not merely on account of the entire coin- 

 cidence between the results of my own inquiries into the structure of Polystomella crispa and 

 those of my accomplished predecessor, but also because our views are in every respect borne 

 out by the structure of the much larger and more highly developed form of PoJijalomdla which 

 I am presently to describe. 



470. As this type presents itself under a variety of forms, which differ not only in 

 external features, but in internal structure, it will be desirable to give sepai'ate descriptions 

 of two of its most characteristic examples, known as P. criyja and P. cratimlata ; the former of 

 which is a common inhabitant of British and other temperate seas, whilst the latter, which is a 



