60 PROCEEDINGS COTTESWOLD CLUB 1907 
The posterior beak-slopes of different forms afford inte- 
resting evidence of the course of evolution. When the beak- 
slopes are concave, as in C. cor, they indicate a narrower 
form becoming wider. In C. xummata, and in C. ds, the 
beak-slopes are concavi-fastigate, shewing that the C. cor 
course of development still affected the early stages of these 
forms. But in most of the other forms concavifastigation 
is so soon done with as to be hardly noticeable : the beak- 
slopes are practically planifastigate, indicating that acceler- 
ation into the broad stage has obliterated the C. cov-phase. 
In C. sestertzus the beak slopes are even convexifastigate, 
shewing that the broad form has influenced quite the early 
stage, and that afterwards return to the elongate stage 
takes effect. 
The idea that C. cor is a variety of C. xumzsmatis can- 
not be entertained: it is geologically earlier, and it is, 
in regard to most of its characters, a form in an earlier 
stage of development. Nor can C. xe«mzsmadis be regarded 
as the mutation of C. cor. it is a form which passed 
through an adolescent C. coy-stage, and probably through 
a C. orbicularis-stage in its course of development. 
Details of Synonymy 
—, Terebratula, Brug. Ency. cexl, 1 = C. numismalis. 
causoniana, Tereb., VOrbigny = °C. causoniana. 
conocollis, ’Waldheimia, Rau, xxxiv, 12-15 = C. conocollis. 
n xxxiv, 16 = C, paupercula. 
cor, Tenebri : Daviasan. Annals = a cor. 
" i" Valenciennes (Lamarck) = C. cor. 
»  Waldheimia, Davidson, 1884, xix, 16 = C. sp. 
» Zeilleria, Bayle = |G, dives. 
numismalis, Terebr., Davidson, Annals = C. pernummus. 
" " " Pal. Soc. v, 4 = C. nummus. 
" " " " V, 6 = 2G. dives. 
" " " v, 6,7 = ?C. orbicularis. 
" n Gieastont. Jura, xvii, 37, 38, 40 = C. opulenta. 
" " " » xvii, 39 = C. pernumismalis. 
