452 ME. A. WADE ON THE LLANDOVEEY AND [Aug. I9II, 



shape of the valve, in the fact that the dorsal margins of the loop 

 are not so prominent, and in the presence of a slight tubercle 

 within the sulcus enclosed by the loop. I have figured Ulrich's 

 species for comparison. 



Fig. 9. — Melanella hemidiscus gen. et sp. nov. (a Sf b) and 

 Jone sella crepidiformis Ulrich (c). 



[Magnification = about 15 diameters.] 



Horizon and locality. — Black shales of Gwern-y-brain. 



In addition to the species just described, several others occur in 

 the Gwern-y-brain Shales, which are new to British geology. The 

 following brief notes will serve to record their chief characters : — 



Peimitiella unicoenis Ulrich. (PI. XXXVI, figs. 4 & 5.) 



This species has already been described by the late Prof. Jones 

 from specimens obtained by Bickerton Morgan from the Gwern-y- 

 brain Shales. There are, however, one or two distinct varieties 

 present which are referable to this form. 



Yar. 1 differs from the type-form in having a tubercle placed 

 centrally, as well as a sulcus in the anterior fourth of the hinge - 

 line. (See PI. XXXYI, fig. 4.) 



Yar. 2 is distinctly punctate, with one large pore placed in a 

 central position anteriorly with a slight sulcus behind it. (See 

 PI. XXXYI, fig. 5. Unfortunately the punctation does not show 

 distinctly enough in the figures reproduced in this Plate.) 



Peimitia uleichi Jones. 



This species corresponds in shape and size with the late Prof. 

 Jones's specimen, but differs in having a slight sulcus about half- 

 way along the hinge-line. 



Peimitia tttmidula Ulrich. 



This specimen is a trifle larger than the species described by 

 Ulrich, otherwise it possesses similar characters. 



Ctenobolina cf. ciliata Emmons. (PI. XXXYI, fig. 6.) 



The shales provided both a typical specimen and a distinct 

 variety, which is smaller and differs in the anterior ridge being 

 small and separated from the central ridge. It may almost be 

 considered a new species. 



