212 MRS. JANE LONGSTAEE ON [May I909, 



L. rugiferurn, the third ' type,' is also represented by two forms, 

 one Carboniferous and the other Devonian. The latter received the 

 name L. anglicum from A. d'Orbigny, 1 and the former was described 

 as Melania rugifera by Phillips. 2 Although both these shells belong 

 to the family Loxonematidae, they cannot be referred to the genus 

 Loxonema s. s., but must find a place in the subgenus Zygopleura, 

 Koken. 3 



Not only has Phillips associated with Loxonema several forms 

 which do not bear the characteristics of the genus as defined by him, 

 but succeeding palaeontologists have done the same. Prof. Koken, 

 however, and several recent authors, perceiving this error, have 

 created new genera and subgenera for these shells. As this paper 

 simply deals with Ordovician and Silurian species, but few subgenera 

 need be mentioned : these are Rliabdostropha, Donald, 4 and Stylo- 

 nema, Perner. 5 



It is possible that a distinct group should be made for such forms 

 as the Devonian L. sinuosum, Phill. (cornubicum), L. nexile (Sow.), 

 L. Jiennahianum (Sow.), etc., having more flattened whorls strongly 

 adpressed at the suture, with an angularity on the body- whorl, and 

 coarser and less strongly-bent lines of growth than the genotype. 



Genus Loxonema, Phill. emend. 



Diagnosi s. — Shell elongated, turriculated, consisting of numerous 

 whorls. Whorls convex or slightly flattened, their upper edges 

 adpressed against the next above. No spiral band ; ornamentation 

 consisting of sigmoidal lines or threads. Aperture oblong, attenuated 

 above, effused below, outer edge sigmoidal. No umbilicus. 



Genotype, Loxonema sinuosum, Sow. 



Dimensions. — The British Proterozoic species range from about 

 20 to about 65 millimetres in length. 



Remarks and relationship. — It is always difficult to ascertain 

 the affinities of Palaeozoic families, owing to the imperfect pre- 

 servation of their representatives, and to this the Loxonematidae are 

 no exception. The earlier palaeontologists placed the genus Loxo- 

 nema in different families, such as the Pyramidellidae, Euomphalidae, 

 or Pseudomelaniidas, according to their several views of its affinities. 

 Prof. Koken considers that it and several closely allied genera should, 

 constitute a distinct family, and most recent palaeontologists follow 

 his example. He also thinks that Loxonema, Murchisonia, and 

 Ectomaria are nearly related. The typical Loxonema certainly 

 bears great resemblance to some of the genera and subgenera into 

 which the Murchisoniidae have been divided ; and more especially to 

 Hormotoma (where the whorls are smooth and the lines of growth 

 may be traced from suture to suture), but this genus differs in having 



1 ' Prodr. Paleont. Strat.' vol. i (1850) p. 62. 



2 ' Illustr. Geol. Yorks.' vol. ii (1836) p. 229 & pi. xvi, fig. 26. 

 s ' Die Leitfossilien ' Leipzig, 1896, p. 108. 



4 Quart. Journ. Geol. Soc. vol. lxi (1905) p. 565. 



5 ' Syst. Sil. Centre Bokeme,' pt. i, vol. iv, Gasteropodes, par J. Perner, 

 tome ii (1907) p. 325. 



