260 Prof. T. R. Jones and Mr. J. W. Kirkbj on the 



Found by Dr. H. B. Holl, F.G.S., in Carboniferous Lime- 

 stone, Great Ormes Head. 



This and the two following unisulcate forms have the aspect 

 of Primitia, but further research is necessary before we can 

 determine if they belong to that genus or to our new group 

 Beyrichiella (Geol. Mag., Oct. 1886). 



26. Beyrichiella (?) reticosa, sp. nov. 

 (PI. YIII. figs. 15, 16 a, 16 5, 16 c.) 



Obliquely subovate ; valves compressed in front, widest 

 behind, and thus with a subcuneiform lateral contour. A 

 deep and narrow sulcus marks the centre of each valve, and 

 the postero-dorsal region of each is sharply ridged, leaving a 

 depressed dorsal area between ; right valve slightly larger 

 than the left. Surface regularly reticulate. Length vq to 

 aV inch. 



The angulate postero-dorsal region of this species (not well 

 shown in tig. 16 Z*) suggests relationship to Beyrichiella; fur- 

 ther knowledge of it may probably cause its removal to that 

 genus. 



Collected by Mr. James Bennie in the Carboniferous-Lime- 

 stone series at Whitebaulks, Linlithgowshire ; and Abden, 

 Fifeshire. 



27. Beyrichiella (?) ventricornis, J. & K. 

 (PI. VIIL figs. 17, 18 a, ISb, 18 c.) 



Cythere ventricornis, J. & K., MS. 1867, Trans. Geol. Soc. Glasgow, 

 vol. ii. p. 223. 



Obliquely subovate ; convex, especially below ; dorsal 

 border straight ; ventral border convex ; anterior extremity 

 high and rounded, protuberant below ; posterior extremity 

 smaller than the other and curving backward below. A 

 simple shallow sulcus extends from the dorsal border less than 

 halfway across each valve, near the centre ; a short spine is 

 always present on the postero-ventral region, and very rarely 

 another is seen at the postero-dorsal angle. Lateral contour 

 ovate, wide behind, narrow in front. Valves nearly equal; 

 surface smooth. Length -^ to yj inch. 



We place this species in Beyrichiella on account of its Leper- 

 ditioid outline, unisulcate valves, and probable dorsal crests. 

 It belongs, however, to a very simple type of the genus. 



Mr. John Young discovered this species, which is a charac- 

 teristic form of the Carboniferous-Limestone series in Scotland, 

 and of the Yoredale rocks in England. 



Localities. St. Monans, Liverteil Quarry, Charlesfown 



