220 BRITISH AVONIAN CONODONT FAUNAS 
Siphonodella isosticha (Cooper) 
Plate: 12, “hesvoaswb, 11a, b 
1939 Siphonognathus isosticha Cooper : 409, Pl. 41, figs. 9, 10. 
1962 Siphonodella n. sp. A Collinson, Scott & Rexroad : 7, fig. 4. 
1962 Siphonodella obsoleta Cooper ; Miiller (partim) : 1388, fig. 4 only. 
1964 Siphonodella isosticha (Cooper) Rexroad & Scott : 44, Pl. 3, figs. 21-23. 
1965 Siphonodella isosticha (Cooper) Ethington : 587, Pl. 67, figs. 15, 17, 
MATERIAL. 3 specimens : figured, X 534, X 535. 
RANGE. North Crop KL 16-KL 19. 
Description. The platform is narrow and elongate being broadest at its mid- 
point. Ornament is lacking except for a medial nodose carina, two short anterior 
rostral ridges, a few scattered nodes on the narrow inner platform, and incipient 
transverse denticles on the margin of some specimens (PI. 12, fig. 11a). The basal 
cavity is minute, and the whole unit keeled. 
REMARKS. Rexroad & Scott (1964 : 44) suggested that this species arose from 
S. obsoleta Hass by reduction of the outer rostral ridge and platform ornament, but 
they pointed out that the juveniles of the two species are very similar. All our 
specimens appear to be young forms and they could be assigned either to S. obsoleta 
or S. zsosticha, but absence of platform ornament in the largest specimen suggests 
that they should be placed in S. zsosticha. 
Siphonodella obsoleta Hass 
Plate 12, figs. 13a-c 
1959 Szphonodella obsoleta Hass : 392, Pl. 47, figs. 1, 2. 
1962 Siphonodella aff. S. obsoleta Hass ; Collinson, Scott & Rexroad : 7, chart 2. 
1964 Siphonodella obsoleta Hass ; Rexroad & Scott: 45, Pl. 3, fig. 25. 
1964 Siphonodella obsoleta Hass [Nass in text] ; Budurov & Tschurnev : PI. V, figs. 5a-c, 
Ita, b, 13a, b, 14-17, 19. 
MATERIAL. 2 Specimens : figured, X 5306. 
RANGE. North Crop KL 16-KL to. 
Posterior 
Platform 
Lateral ridges 
Carina 
——_—— Outer side 
Nodes Rostral ridge 
Anterior blade 
Fic. 45. Siphonodella sp. showing morphological terms used in the text. 
