part 2] SYlilJS'GOTHYRJS AJSTD SPIMFERINA. 201 



also results in the disappearance of the last three or four costse, 

 giving the impression that there are only six or seven bold plications 

 on each side of the Held. 



In exfoliated specimens the costse appear to be stouter and less 

 angular than when the shell is preserved. Judged by the figures, 

 the specimens referred to by M'Coy as Spirifera decemcostata 

 and $p, mesnyonia were in all probability exfoliated examples of 

 Tyiothyrix laminosa ; but, as neither of these forms is adequately 

 defined, by M 'Coy's description and figures, and as the original 

 specimens are no longer in existence, 1 the names are best regarded 

 purely as-'syhonyms of that species. 



M'Coy said of the species ' mesial hollow produced when old 

 into a long; tongue-shaped, flattened lobe, 12 and Davidson figured a 

 form possessing that character, which is, however, not of common 

 occurrence. 



Davidson's figures are greatly restored and idealized, and appear 

 to have been based upon three imperfect specimens now in the 

 Sedgwick Museum. These I have been able to examine through 

 the kindness of Dr. F. R. Cowper Reed, and they bear very little 

 resemblance to the figures. Dr. Reed wrote concerning them : — 



' Indeed, unless we knew that these were the actual specimens which he 

 (Davidson) used, and to which he referred, one might hesitate to accept 

 thenj as the types.' fin litteris.) 



'Apart from the prolongation of the floor of the sinus, the speci- 

 mens are nearer to T. suhconica than to T. laminosa in the height 

 and curvature of the area. The locality is given as Derbyshire, 

 but the horizon is not known. 



Comparison with T. suhconica. — Tylothyris laminosa and 

 its mutations are readily distinguished from T. suhconica by the 

 greater concavity of the area (compare figs. 4 a, 4 h, & 4 d, p. 199). 

 In T. suhconica the sinus and the cost* are more angular, the line 

 along the base of the sinus less curved, and the fold less elevated 

 than in T. laminosa. 



Shells incorrectly referred to Tylothyris laminosa 

 (M'Coy). — A number of shells which do not really belong to that 

 species have been referred to T. laminosa, on account of their 

 laminose ornament. Two of these are of sufficient interest to be 

 dealt with separately: — 



(1) ' Spiriferina la mi no sa ' from beds of Dibunophyllum age at 

 Eedesdale (Northumberland) and other localities, so named by King ; 



1 These specimens, together with the holotype of M'Coy' s Sp. laminosa and 

 others, were formerly in the ' Griffith Collection,' but their whereabouts are 

 now unknown. Dr. R. F. Scharif very kindly caused a fresh search to be 

 made for them in the collection of the National Museum, Dublin, but without 

 success ; and they have not hitherto been recognized in any public collection, 

 although Davidson speaks of having examined the type of Sp. decemcostata 

 |-1] p. 43. In all probability the original figures were, as was often the case, 

 idealized, so that actual specimens, if met with, would pass unrecognized. 



- M'Coy [21] p. 426. 



p2 



