STROPHOMENIDtE. 295 



Strophomena deltoidea, var. (3, undata, M'Cot/. PI. XXXIX, figs. 23 and 24. 



Oethis undata, M'Coy. Sil. Foss. Ireland, pi. iii, fig. 21, 1846. 

 Strophomena deltoidea, var. /3, undata, M'Goy. Brit. Pal. Foss., p. 234, pi. in, 

 figs. 38 and 39, 1852. 



I know SO little of this shell, never having seen more of it than the specimens 

 described by M'Coy, that I must content myself by reproducing his figures and observa- 

 tions. It was described by him, in 1846, from a large flattened, and, to my eye, obscure 

 impression; but in 1852 the distinguished Irish palaeontologist informs us that his 

 species is a simple variety of Strophomena deltoidea, from which it would seem to difier 

 in various ways, and until its interior is known I cannot say whether it is or not a 

 variety of St. deltoidea, to which it is provisionally referred. " This apparently distinct shell, 

 " observes M'Coy,'' is semioval, about one and a half inches long, with a narrow deflected 

 border, rarely half an inch deep ; the visceral disk gently convex, ragged, with twelve 

 or fourteen very large, undulating, concentric wrinkles, sometimes much interrupted, and 

 nearly obsolete (like the type I originally figured), crossed by radiating obtuse striae, 

 which vary singularly in size in the different specimens, alike in all other respects — one 

 specimen having only ten striae in two lines at four lines from the beak, and another 

 having twenty-four, and many specimens having the intermediate numbers ; the lines 

 are often sub-equal, or in all the middle portion towards the margin every 5th or 7th 

 considerably larger than the rest. In the specimens I originally described, the surface 

 seemed smooth, except some faint traces which I mentioned of longitudinal striae ; the 

 better specimens now before me are all distinctly striated, but so much alike in other 

 respects that I have no doubt of their identity, the geological position of each being 

 alike. The specimens of this variety, which show the dental lamellae, seem to have 

 them more divergent and the muscular impressions wider than in the typical form. 

 Some specimens of this variety have upwards of twenty concentric rows of faint, inter- 

 rupted, concentric undulations, giving a curious rippled appearance to the surface, from 

 which I named the species, when I believed it distinct.'' 



Position and Locality. Var. /3, undata. Common in the Bala Limestone of 

 Llandeilo, Caermarthenshire ; of LI wyn-y-ci, north-west of Bala ; of Pont-y-Glyn-Diffwys, 

 west of Corwen ; Bala Schists of Bryn Melyn, and Gelli Grin, Bala, Merionethshire ; 

 of Cyrn-y-brain, west of Wrexham, Denbighshire ; Bala Sandstone of Alt-y- Anker, Meifod, 

 Montgomeryshire ; Bala Limestone of Coniston, North Lancashire ; ? in olive shale of 

 Coed Sion, Llangadoc, South Wales (M'Coy). 



This is a much larger shell than Strophomena deltoidea, and it is very desirable that 

 a good series of specimens showing the external and, above all, the internal characters 

 should be sought for in the localities above recorded by Prof. M'Coy. 



