7G 
or less arclied according to the position they occupy. The heak of the ventral 
valve is small, slightly curved and little prominent, hut pointed ; the sinus is 
usually rather large and generally composed of four mesial folds separated 
from the lateral folds by a rih which is much more developed than the 
adjacent ones ; in adult individuals this sinus rises sharply towards the front 
at about the middle point of its length. The dorsal valve is fairly regularly 
arched, the median lobe is not always very strongly marked; the number of 
folds that partake in the formation of this lobe is always greater by one than 
that comprised in the sinus. 
Melations mid Differences . — After comparing a large number of 
Devonian with Carboniferous specimens of this form, I have not been able to 
find a sufficiently appreciable and constant difference between them to enable 
me to assert that they belong to different species, as has been stated by 
A. d’Orbigny ; as regards proof to the contrary, I side wdth J. Phillips 
and Mr. T. Davidson who consider them both identical. In making this 
statement, it must he admitted also that the Devonian species vary in their 
shape as much as do the Carboniferous ; at the same time it was difficult for 
me to believe that R. Tethys, Sappho and Dotis, J. Hall, are anything but 
varieties of B. pleurodon. However, I do not wish to speak definitely on 
this point as I am absolutely without material for comparisons. 
Horizon and Localities . — In Belgium this species is found in the 
Upper Devonian and in the United States in the Chemung Group. In 
Australia it is associated with Sp. disjunctus, Sow., in a yellow sandstone at 
Sofala ; it is very abundant in a greyish sandstone at Mount Lamhie, near 
Yass.^ 
2. PvHYNCHONELLA PUGNTJS ? Martin. 
Conchyliolithes Anomites pug mis ? Martin, 1809, Petrif. Derb., p. 13, pi. 22, fig. 4, 5. 
Atrypa pugntlS, Sowerby, 1840, Trans. Geol. Soc. Lend., V (2), pi. 56, fig. 15-18. 
Terehratula „ J. PHllips, 1841, Pal. Poss. Coiwall, p. 87, pi. 35, fig. 156. 
,, anisodonta. Idem, 1841, Hid., p. 85, pi. 34, fig. 154. 
Bhynchonella pugniis. T. Davidson, 1865, Mon. Brit. Dev. Bracb., p. 63, pi. 12, fig. 12-14, 
and pi. 13, fig. 8-10. 
The shape and characters of this species are sufficiently well known to 
enable me to dispense with repeating them here. I will confine myself to 
' [Mt. Lanibie is near EyJal on the Western Railway Line, whereas Yass is on the Sonthern,- — W.S.D.] 
