310 
DEVONIAN FAUNA. 
in which the first seven whorls exactly correspond with Goldfiiss's figure of the 
variety M. intermedia, while the other two whorls change from the short, rounded, 
nodulous, to the acutely triangular, smooth style, and have very narrow sinus- 
bands, so that they are much beyond the extremes of his figures of the varieties 
M. hilineata and M. angulata. Another of Mr. Vicary's specimens has its whorls 
generally smooth, but they occasionally become tuberculous for a short distance. 
The coiling of the spire is frequently irregular, so that its contour becomes 
slanting or unsymmetrical, convex or concave. Specimens also differ very greatly 
in elevation, and in the size of the body- whorl, some having it higher and more 
capacious than the rest of the spire, while in others it is less than a quarter of the 
total height. Again the shape of the section of the whorls and the amount of 
tuberculation is extremely variable, but, as observed above, these points sometimes 
change so much in the same specimen that it is easy to see that they are not 
specifically important. In spite of all these differences there is so much character 
in the species that, except perhaps in one or two cases, it is very easy to define its 
bounds. The only other Devonshire species which approaches it is M. Vicariana, 
but that shell shows several clear distinctions, and I have seen no passage speci- 
mens between them. 
On the other hand there is a recognisable amount of centering around certain 
shapes, a few of which are enumerated below ; but in all probability these were 
not hereditary varieties, but only common accidental shapes of the shell. 
1. Group spinosa. Shell often very large, generally much elevated. Upper 
row of nodules few and very coarse ; lower row sometimes indistinct, sometimes 
like the upper row. Whorls subquadrate, PI. XXIX, figs. 1 — 10. 
Cf. M. s^jinosa, Sowerby, and Phillips (pars), M. coronata, bigrannlosa, and 
hinodosa, d'Archiac and de Verneuil. 
2. Group curta. Shell short, body-whorl generally longer than the spire. 
Upper row of nodules few and very coarse ; lower row absent. Whorls sub- 
globose. PI. XXIX, figs. 14—16. 
Cf. M. sj^inosa, Phillips (pars). 
3. Group intermedia. Shell rather large, regular, elevated, conical. Upper 
row of nodules small, and numerous, and indistinct. Whorls subquadrate. 
PI. XXX, figs. 1—4. 
Cf. M. hilineata ? Phillips ; M. intermedia, d'Archiac and de Verneuil. 
4. Group angulata. Shell elongate, irregularly coiled. Whorls triangular, not 
nodulous. Sinus-band prominent, strongly ridged, situate at the widest and 
central line of the whorl to which the sides slope concavely above and below. 
PI. XXX, figs. 5—10. 
Cf. M. angulata and geminata, Phillips; M. angulata, d'Archiac and de Verneuil ; 
M. angulata (pars) and nerinxa, Sandbergcr. 
