Vol. 65.] THE GESTJ3 LOXOKEMA. 211 



that it is distinct from the Devonian shell so named by Phillips. 

 Mr. "VVhidborne, 1 however, thinks them identical. There is no 

 doubt, nevertheless, about their being different, and the question 

 therefore arises as to the shell upon which Phillips founded his 

 diagnosis, since that must be regarded as the genotype. 



It has been suggested to me that Phillips must have intended the 

 Devonian form which he had by him as the genotype ; but, as he 

 does not clearly state this, he leaves it to those who follow to decide 

 the matter. He quotes ' L. sinuosa ' as the first ' type ' before 

 he gives the specific description of his shell ; therefore he must 

 evidently refer to Sowerby's form, but his generic description 

 is probably founded on both shells. Succeeding palaeontologists 

 have adopted the name L. sinuosum as the genotype, though not 

 always stating which form they meant, for most of them evidently 

 did not realize that two distinct shells were indicated by one name. 

 This seems to have been the case with both S. P. "Woodward and 

 P. Fischer. The former 2 quotes as type ' L. sinuata, TJ. Devonian, 

 Petherwin,' without stating to whom the species is referable. 

 When P. Schmidt 3 mentions L. sinuata he evidently means L. sinu- 

 osum (Sow.), as he refers to the figure of that shell in the ' Silurian 

 System,' and it is highly probable that Woodward does the 

 same. Fischer 4 gives for type 'Z/. sinuosum, Sow. Devonien.' 

 Those who have most deeply studied the Palaeozoic Gasteropoda, 

 such as Lindstrom, Koken, and Perner, appear to have taken it for 

 granted that L. sinuosum (Sow.) was the genotype, for they do 

 not discuss the claim of the Devonian form to be considered as 

 such. It seems advisable to follow their example, as likely to cause 

 least confusion : for, if the Devonian shell were substituted, it would 

 necessitate the introduction of a new name for the genotype and 

 upset much good work. 



If L. sinuosum (Sow.) be regarded as the genotype of the genus 

 Loxonema sensu stricto, it is clear that the other two ' types ' 

 mentioned by Phillips cannot remain in the genus. The second 

 ' type ' is represented by L. tumiclum and L. linctum ; the latter 

 species belongs to the genus MacrochUina. Bayle. 6 Two distinct 

 species are named tumida by Phillips, one Carboniferous, the other 

 Devonian. The former as represented in the figure 6 does not 

 appear to have had sigmoidal lines of growth. The holotype is not 

 in the Gilbertson Collection at the British Museum, and the 

 only specimen contained in that collection has not the surface pre- 

 served. I have not been able to find the holotype of the Devonian 

 form ; but, judging by the figure, 7 it is very different from L. sinuosum 

 in character. 



1 ' Devonian Fauna of the South of England ' pt. iii, Monogr. Palseentogr. 

 Soc. vol. xliv (1890-91) p. 176. 



2 ' A Manual of the Mollusea ' 2nd ed. (1871) p. 141. 



3 Archiv fur die Naturkunde Liv- Ehst- & Kurlands' ser. 1, vol. ii (1858) 

 p. 202. 



4 ' Manuel de Conchyliologie & de Paleontologie Conchyliologique ' 1885, 

 p. 696. 



5 Whidborne, op. supra cit. p. 163. 



6 'Illustr. Geol. Yorks.' vol. ii (1836) pi. xvi, fig. 2 & p. 229. 



7 ' Pal. Foss. Cornwall, &c.' 1841, pi. xxxyiii, fig. 186 & p. 223. 



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