148 BRITISH AVONIAN CONODONT FAUNAS 
recurved, but their axes are straight and sharply pointed ; they have sharp anterior 
and posterior edges and strongly convex lateral faces, their proximal portions tending 
to become flatter towards their apices ; they are about four to five times as long as 
the other denticles on the unit. The inner lateral face of the lateral bar is marked by 
a callus, which is not conspicuous and does not extend far up the lateral face : the 
bar decreases in width posteriorly and its posterior end is marked by a very small 
denticle, the posterior aboral margin being bluntly rounded ; the bar may be very 
slightly flexed outward in a vertical plane, but it is essentially straight. 
The posterior bar is of unknown length; it bears at least one small denticle near its 
junction with the lateral bar. It is excavated by a narrow groove which extends 
continuously below the lateral bar. 
REMARKS. Rexroad & Collinson (1963 : 21), described forms closely similar to 
this species, but did not include them in the genus Magnilaterella. They did not 
state the reasons for this exclusion, but these presumably involve the relatively 
slight difference in the form of the basal cavity, which in the present specimens tends 
to be medial rather than lateral on the two bars, the restricted nature of the callus, 
and the fact that the posterior denticle of the lateral bar is not the largest of those 
developed. 
Other specimens described above in the present paper show that none of these 
characteristics is wholly distinctive of the genus Magnilaterella. Some species 
which are, on all other morphological criteria, “‘ good ’’ species of the genus, do not 
have the posterior denticle more strongly developed than the rest of the series, and 
the form of the callus is a highly variable feature ; it, therefore, seems to us that there 
is no good reason for excluding this species from the genus. 
Magnilaterella robusta Rexroad & Collinson 
Plate 31, figs. 25, 26, 27 
1941 Lonchodina sp. Branson & Mehl (partim) : 171, Pl. 5, fig. to only. 
1956 Metalonchodina ? sp. Elias: 124, Pl. 5, fig. 3. 
1957 Genus Indeterminate Rexroad (partim) : 42, Pl. 4, figs. 19-21 only. 
1958 Genus Indeterminate Rexroad : 26, Pl. 5, figs. 1, 2. 
1963 Magnilaterella vobusta Rexroad & Collinson : 14, Pl. 2, figs. 4, 5, 9, text-figs. 3, 4. 
1964 Magnilaterella vobusta Rexroad & Collinson ; Rexroad & Furnish : 673, Pl. 111, figs. 
27-31. 
1965 Magnilaterella vobusta Rexroad & Collinson ; Rexroad & Nicoll: 22, 23, Pl. 1, figs. 
TOLL: 
MATERIAL. 3 Specimens : figured, X 528, X 529, X 548. 
RANGE. Scotland Samples DUN 78-79. 
DeEscrRIPTION. Well preserved specimens from our Scottish faunas are very 
closely similar to those illustrated and described by Rexroad and Collinson. The 
inner lateral process is short and stout, and is strongly recurved and very strongly 
arched. It bears up to 6 denticles, those near the apex being the largest. The 
posterior bar is small and relatively straight. It is strongly flexed and bears only 
I or 2 denticles, that nearest the anterior end being the largest. 
