130 BRITISH AVONIAN CONODONT FAUNAS 
the general symmetry of this species, a feature that is so striking that it led Rexroad 
in his initialdescription to assign it to the genus Tvichonodella. The denticles tend to 
increase in size towards the distal third of the bars, and the apical denticle tends to 
stand erect between the converging denticles of the anterior and posterior bars. 
There is a feeble basal flange below the apical denticle. 
Hindeodus sp. 
Plate 22, figs. 17a-20b 
1964 Hindeodus sp. Rexroad & Furnish : 672, Pl. 111, fig. 11. 
MATERIAL. I0 specimens : figured, X 189, X 191, X 188, X Igo. 
RANGE. Scotland HOSIE 2A~-2B. 
DESCRIPTION. Certain of the present specimens, although showing minor varia- 
tions in form, are obviously closely related to one another. These specimens possess 
a short, deep, posterior bar which has a straight aboral margin in lateral view. The 
bar is slightly flexed inwards longitudinally and its oral surface bears at least ro 
confluent denticles, only their apices being discrete and bluntly pointed. They are 
inclined gently posteriorly and are more or less of uniform size. The apical denticle 
is about twice as long as the largest denticles of the rest of the bar. It is basally 
confluent to those on either side of it and has sharp anterior and posterior edges and a 
strongly biconvex cross-section. The anterior bar is shorter than the posterior, and 
is gently concave basally in lateral view. Its oral surface bears a series of about 5 
denticles, similar in form to those of the posterior bar, which tend to decrease in size 
anteriorly and which are recurved so that they lie sub-parallel to the apical denticle. 
It makes an angle of about 90°-110° with the posterior bar. The denticles of the 
anterior bar tend on the whole to be rather broader than those of the posterior. The 
inner lateral face of the anterior bar is gently concave. In outer lateral view the 
whole unit is seen to be gently arched inwardly and its outer lateral face is flat to 
gently convex. There is a slightly expanded cavity below the apical denticle and 
very fine longitudinal grooves extend along the lengths of the two bars. 
Genus KLADOGNATAHUS Rexroad 1958 
1958 Kladognathus Rexroad : 19 (pro Cladognathus Rexroad 1957, 28 non Burmeister 1847). 
1961 Cladognathodus Rexroad & Collinson : 6 (abs. syn.). 
TYPE SPECIES. Cladognathus prima Rexroad. 
This genus was first described by Rexroad in 1957 under the name Cladognathus, a 
name later found to be a homonym of one used by Burmeister in 1847. The name 
Kladognathus was proposed by Rexroad 1958, as a substitute. Rexroad & Collinson 
(1961 : 6), however, changed this to Cladognathodus because they suggested that the 
replacement of a letter “‘ C”’ by a letter “ K ” did not represent a valid name change 
under the rules of nomenclature. Article 56A of the International Code makes it 
clear, however, that a difference of even one letter in the spelling of generic names 
represents a valid distinction between them. The name Kladognathus Rexroad 1958 
