110 BRITISH AVONIAN CONODONT FAUNAS 
Genus HIBBARDELLA Ulrich & Bassler 1926 
1925 Hibbardella Bassler ; 219 (nom. nud.). 
1926 Hibbardella Ulrich & Bassler : 37. 
TYPE SPECIES. Prioniodus angulatus Hinde 1879. 
Description. Ulrich & Bassler established the genus Hzbbardella with the type 
species Hibbardella (Prioniodus) angulata Hinde for a group of arched blade-like 
conodonts in which a striking apical denticle was developed. The whole structure 
was bilaterally symmetrical and the apical denticle sharp-edged, erect and greatly 
elongated. The denticles of the anterior bar were relatively few in number, widely 
spaced and turned slightly inward. Ulrich & Bassler did not mention the character 
of the basal cavity, nor the possibility of the development of a denticulated posterior 
bar. Topotype material studied by Dr. J. W. Huddle, of which he has kindly 
provided us with photographs, shows that both these features are well preserved. A 
more or less short stout denticulated posterior bar is developed, and there is a thin 
groove-like basal cavity which extends along both the anterior bars and the posterior 
bar. 
Subsequent authors have erected several genera of essentially similar general form 
which have been distinguished on minor morphological differences. These include 
Roundya Hass (1953) Ellisonia Miller (1956) and possibly also Diplododella Bassler 
(1925). There has been some discussion as to the validity of these and other genera, 
especially the genus Tvichonodella. The most satisfactory solution to the present 
situation seems to be to subdivide the genus Hzbbardella into three subgenera, based 
on the following characteristics : 
1. HIBBARDELLA< s.s. arched denticulated conodonts, with a bilaterally 
symmetrical anterior bar and a strongly developed apical denticle. The 
apical denticle is strongly compressed antero-posteriorly and has sharp 
\ - Main cusp 
a 
\ \ 4 A. VI j 
Lateral bar WW ; Af \Z 
Posterior bar 
Denticles 
jen Lotenol ibair 
\ 
Position of basal cavity 
Anterior view 
Fic. 23. Huibbardella sp. showing morphological terms used in the text. 
