FROM NORTHWESTERN EUROPE 91 
Diacnosis. Medium to large Septaliphoria ; 9-15 very coarse subangular ribs ; 
no smooth area posteriorly ; uniplicate or asymmetrical ; conjunct deltidial plates ; 
strong suberect beak ; crura radulifer. 
STRATIGRAPHICAL RANGE. Oxfordian—mariae and cordatum zone ; the Lower 
Calcareous Grit of Yorkshire. 
TYPE SPECIMEN. Holotype, BB. 45394, selected from a box of specimens in the 
collection of the B.M.(N.H.) with the locality given as ‘“‘ Hutton Bushell, Beedale, 
Yorkshire ”’. 
DIMENSIONS OF HOLOTYPE. Length 2-61 cm, thickness 1-78 cm, width 2-90 cm. 
MATERIAL. About 100 specimens, all from the collection of the B.M.(N.H.) 
B. 26924, B. 26903. 
DESCRIPTION. External characters. The width is usually greater than the 
length, with the greatest width well towards the anterior giving the species a sub- 
pentagonal to subtriangular outline. 
The beak is strongly developed in the smaller, more triangular specimens but is 
much less pronounced in the larger ones. Clearly marked beak ridges bound the 
strongly incurved interarea. An oval, submesothyridid pedicle opening is flanked 
by strongly conjunct deltidial plates. 
The shell ornament consists solely of very coarse, steep, subangular ribs ; the size 
and coarseness of the ribbing readily distinguishes the species from S. avduennensis. 
DIMENSIONS OF FIGURED SPECIMENS. 
length thickness width 
2°58 cm 1-85 cm 2°90 cm 
2°40 cm 1-O7 cin 2°54 cm 
Internal characters. Pedicle valve. The dental lamellae are subparallel and 
relatively short, breaking away from the valve wall well before the insertion of the 
teeth, as seen in transverse section. The teeth are strong and there are well 
developed lateral denticulae. 
Brachial valve. A septalium is present and consists of strong septalial plates and 
and a relatively weak median septum. The sockets show only weak crenulations ; 
inner and outer socket ridges are well developed. 
The crura, which have clearly differentiated bases, are radulifer and curve towards 
the pedicle valve. At their distal ends they develop the curious processes which are 
also found in S. avduennensis. 
DistRIBuTION. As far as is known, the species has only been recorded from the 
type locality and from Filey Brigg (E. F. Owen, personal communication 1966). 
REMARKS. The species only appears to have been mentioned twice in the litera- 
ture. In 1878 Davidson tentatively referred the specimen he figured from Wykham 
to Rhynchonella lacunosa Schlotheim and in 1917, Rollier suggested that Davidson’s 
specimen might be R. helvetica (Schloth.). As the species does not belong to the 
“lacunosa group”’ and R. helvetica is here regarded as a nomen dubium, a new 
species name has been proposed for these forms from the Lower Calcareous Grit. 
