68 
kindness of Mr. Townsliend W. Hall, of Barnstaple. I trust my learned 
confrere of the Geological Society of London, will allow me to express 
publicly my indebtedness to him. 
Although in the last description I gave of Chonetes Laguessiana^ I 
have already detailed the principal differences that exist between this Carboni- 
ferous species and the Devonian Chonetes Sardrensis, I think it would be 
useful to give them again : — 
Tlie Devonian species never attains the size of the Carboniferous, 
its outline is more regularly semicircular; the number of radiating ribs 
is always less than in a Carboniferous specimen of the same size ; these 
riljs are less prominent and less angular, and the furrows separating them are 
not so deep ; their bifurcations are less numerous ; they are much more 
noticeable on the cardinal edge than in the Carboniferous Chonetes; the 
ventral valve is less convex and consequently the dorsal valve is less concave; 
the muscular impressions in the dorsal valve are less developed, but on the 
other hand the median septum is relatively longer, though less prominent ; 
the granulations that ornament the interior surface of the same valve are less 
noticeable but more numerous; as I have already remarked they are arranged 
in radiating rows corresponding to the ribs on the outer surface, while this 
regularity does not obtain in the Carboniferous species, in which they are 
besides much more developed, chiefly towards the free margins of the shell ; 
finally, the number of spiniform tubes on the hinge line is greater in 
C. Laguessiana than in C. Ilardrensis, on which I have not been able to 
count more than five on either side of the beak, while I seen uj) to eight on 
the Carboniferous species. 
Horizon and Localities. — Aecording to Mr. Davidson this s^^ecies is 
very common in the slates and sandstones of the N ortli of Devonshire, and is not 
rare in the neighbourhood of Barnstaple. It is less common in the Devonian 
Meceptaculites Neptuni, Def., beds of Charlemont near Givet, and of Belgium. 
In Australia Mr. Clarke has collected some good specimens of it in a dark grey 
limestone in the Yass District. They are associated with Spirifer Glmlmmis, 
De Verneuil. A rather badly preserved sj^ecimen found in a yellowish 
psammite at Kempsey belongs perhaps to this species. 
' L. U. de Koninck, Eedierches siir les Anim. Foss., II, p. 40. 
