124 CARBONIFEROUS CORALS AND BRACHIOPODS 
distinctly bounded mesial fold, and indicate a further 
transition towards the ambigua type. 
Cleiotliyris. 
CleiotJiyris Royssii, L’Eveille. 
There are a large number of good specimens in the 
collection, derived from the well-known horizon {“ 40 ft. 
below the Palate Bed”). They exhibit the characteristic 
fringes and agree well v/ith PI. 18, Fig. 8, Dav. 
A mutation, PI. 2, Fig. 2. 
Specimens derived from somewhat higher beds closely 
resemble PI. 18, Fig. 3, Dav. ; they have always lost their 
fringes, but usually exhibit close concentrics, more or less 
crossed by faint longitudinal striae. The beak is usually 
broader and the perforation larger than in the forms found 
lower down. In the absence of the characteristic orna- 
ment, such specimens can only be distinguished from Athyris 
planosulcata, Phill.,by the larger beak, less sloping shoulders, 
and by the presence of a mesial fold. 
The figured specimen from the “ Lower Limestone Shales ” 
shows strong, concentric interruptions of growth and traces 
of faint longitudinal striae on one side. The usual con- 
centric ornament is inconspicuous. 
There are, besides this specimen, three or four others 
(poor specimens) which are derived from the . “ Lower 
Limestone Shales ” or from the Black Rock.” 
Spiriferids. 
Spirifer (Sensu stricto). 
Group of Spirifer hisulcatus, Sow. 
This large group may be considered to include all spirifers 
which exhibit the following characters : — 
In the dorsal valve, a prominent, rounded mesial fold, 
separated from the flanks by more or less pronounced 
grooves ; the ribs on the fold divided into two or three 
