506 MESSES. E. HEEON-ALLEN AND A. EAELAND ON THE 



the groups, we are confronted by the fact that Batsch's fig. 15 c (text-fig. 42, A) is very 

 much more closely allied to his figs. 15 a <& 5 (text-fig. 42, D) (fig. 15 b is merely a 

 section of fig. 15 a), which Brady adopted as the basis of P. flanatus and P. pertusus, 

 than Batsch's figs. Id d & f (text-fig. 42, B, C), which Brady referred to Lamarck's 

 P. {Spirolinites) cyUndracens. It would seem, therefore, that Batsch's name P. (Nau- 

 tilus) arietinus should have been retained for all uncoiled (Spiroline) specimens, 

 whether circular or sub-oval, in the section of the later chambers, and should take 

 precedence over Lamarck's later specific name cylindraceus — excepting as hereinafter 

 used. This separation would be borne out by tlie actual aflBnities which exist between 

 the species planatus (text-fig. 42, D, Batsch fig. 15 a) and arietinus (text-fig. 42, A, Batsch 

 fig. 15 c), which merge into one another by a series of intermediate forms in any 

 gathering in which the genus occurs in abundance, whereas specimens intermediate 

 between the elongate compressed form (text-fig. 42, A, Batsch fig. 15 c) and the elongate 

 circular-sectioned forms (text-fig. 42, B, C, Batsch figs. 15 d,f) are practically non- 

 existent. 



On the other hand, taking Batsch's figs. (?,/ (text-fig. 42, B, C) as a basis for specific 

 distinction, there occurs a continuous diminution in the size and development of the 

 spiroline commencement, and linear development of the later chambers until we 

 arrive at the P. (Spirolinites) cylindraceus of Lamarck (text-fig. 43, E), which is 

 identical with the Nautilus acicularis of Batsch, figs. 16 a, h (text-fig. 43, F) (fig. 16 h is 

 merely a section of fig. 16 a). In this type the spiroline commencement has become 

 almost suppressed. We have taken the trouble to examine d'Orbigny's specimens 

 of Spirolina cylindracea (Lamarck) both in Paris and at La Kochelle, and in all of 

 these the spiroline commencement does not exceed in breadth the diameter of the 

 terminal, or oral, chamber. 



It would seem desirable, therefore, that in future the specific name P. arietinus 

 should be confined to those specimens having a spiral commencement and a produced 

 series of later chambers whether oval or circular in section, irrespective of the relative 

 proportions attained by the spiral commencement, the specific names P. cylindraceus 

 being superfluous excepting as presently suggested for taxonomic purposes, and 

 P. lituus being superfluous altogether. 



The name P. lituus appears in Gmelin's 1788 edition of Linnaeus* on the strength 

 of two references, one to Spengler and the other to Klein, which, however, as we 

 shall see, refer to entirely difi'erent organisms, and the name should therefore lapse as 

 being (to use a legal phrase) "void for uncertainty." But in the 'Challenger' 

 Monograph f Brady figures, under the varietal name P. lituus, certain forms consisting 

 of a number of chambers, circular in section and arranged in a rectilinear series, with- 

 out any trace of a spiral commencement or initial portion of the shell (text-fig. 43, G). 



* L. 1788, SN. p. 3372, no. 13. 



t B. 1884, EC. p. 205, pi. xiii. figs. 24, 25. ' 



