146 DEVONIAN FAUNA. 



genus. The pores of the surface suggest its affinity to the Terebratniidse or to 

 Retzia. The cast (fig. 8 a) shows two short, deep, close, but unconnected subparallel 

 fissures ; on each side of these are shallow, slightly curved grooves, starting close 

 to the apex, and meeting each other just in front of the fissures, so as to form a 

 small ovoid fossula, which perhaps defines the muscle region ; again on each side 

 of this lie rather deep oblique fissures, which seem to be the moulds of the walls of 

 the triangular dental sockets. These features do not tally with those of German 

 specimens of R. stringiceps shown me by Mr. Upfield Green, nor do they seem as if 

 they would be consistent with the structures described by Hall, even in an immature 

 state. On the other hand, I am inclined to think that the shell is most likely to 

 be allied to Rensselldsria or Trigeria, which it appears strongly to resemble in out- 

 ward form and some other points. Consequently, as enough is not yet known 

 about it to give a generic definition, it seems best to leave it provisionally under 

 Renssellderia ; observing, however, that it appears to me most probable that it will 

 be found to require a new generic name when better specimens have been 

 discovered. 



Affinities. R. stringiceps, F. Romer, 1 differs in having much finer and more 

 numerous ribs, i. e. forty instead of twenty. The Ilfracombe shell which 

 Davidson 2 refers to that species is further distinguished by its constant divarication 

 of ribs. Again, the ribs of all the American forms given by Hall and Clarke 

 are much finer and more numerous. 



R. crassicosta, Kock, 3 appears to have the same number of ribs, but, judging 

 from the figures, the ribs are loftier, and the shell much more globose. There is, 

 perhaps, still greater external resemblance in Centronella (Trigeria) Guerangeri, 

 Verneuil, sp., 4 but that is a much smaller shell. 



II. Family SPIRIPERIDJB, King, 1846. 



1. Genus ATHTBIS, M'Coy, 1841. 

 1. ATHYRIS ? sp. Plate XVII, fig. 10. 



Remarks. A few minute, smooth, flattish, elongate, oval shells were obtained 

 by Mr. Porter from Pilton. In shape they appear to be peculiar, but they do not 



1 1844, F. Koiner, ' Ehein. Uebergangsgeb.,' p. 68, pi. i, figs. 6 a, b. 

 3 1864, Davidson, ' Brit. Foss. Brach.,' vol. iii, p. 10, pi. iv, figs. 57. 



3 1880, Gosselet, Esquisse G&l.,' vol. i, pi. i, fig. 20; 1881, Kock, ' Jahrb. f. Min.,' vol. ii, 

 p. 387 ; and 1883, Kayser, ' Jahrb. Preuss. L. A.,' p. 123, pi. v, figs. 25. 



4 1883, CEhlert, 'Bull. Soc. fitud. Sci. Angers' (1883), p. 59, pi. i, fig?. 111; and pi. ii, 

 figs. 16. 



