60 JURASSIC RHYNCHONELLIDS 
although no specific description of A. spinosa was given, he figured a specimen of 
A. spinosa s.s. from the Inferior Oolite of Midford near Bath. 
There was no further discussion of the species until 1936 when Arcelin and Roché 
attempted to disentangle the synonymy, but failed to take account of the literature 
prior to Schlotheim. They described and figured a beautiful series of silicified 
specimens from the Bajocian of Monsard (Saéne et Loire) ; these specimens have 
been examined in the collection of the University of Lyon and appear to belong to 
A. spinosa s.s., although it is difficult to compare the internal structures with those 
of the sectioned material. Also in 1936 Muir-Wood discussed the type of the genus, 
concluding it to be the species referred to by Linnaeus and that this was the “ com- 
mon Inferior Oolite species ’’; in doing this, however, she appears to have overlooked 
the earlier designation of Rollier. She also stated that she considered the spinosa 
of Linnaeus to be congeneric but not conspecific with the form described by Knorr 
and Walch from Muttenz, as specimens from that area were “larger and more 
globose ”’ 
The area of Muttenz now being an industrial suburb of Basel, it is not possible to 
obtain exactly topotypic material ; however, within a few kilometres there are good 
exposures of the Upper Bathonian Varians-Schichten from which the original is 
presumed to have come and the author visited one such exposure at Liestal, collecting 
a good sample of specimens. From the examination of this material, the author 
believes that it should be considered as conspecific with the English species from the 
Inferior Oolite ; specimens from both areas have been sectioned, see text-figs. 21, 22 
and are identical internally. 
Acanthothiris cf. costata Orbigny 
(Pl. 6, figs. 2-4, text-fig. 23) 
1850 Hemithiris costata Orbigny: 286-87. 
1850 Acanthothiris costata Orbigny: 323. 
1910 Hemithiris costata Orbigny; Thevenin: 100, pl. 20, figs. 18-20. 
1917 Acanthothyris costata (Orbigny); Rollier: 74. 
1918 Acanthothiris costata Orbigny; Buckman: 71. 
EMENDED DIAGNOsIs. Medium sized Acanthothiris ; width always greater than 
length ; outline sub-oval ; 25-30 low, rounded ribs ; beak small and tightly 
pressed to the brachial valve ; crura radulifer. 
STRATIGRAPHICAL RANGE. d’Orbigny’s material came from the “ Bajocien”’, 
while the specimens here described are of Upper Bathonian/Lower Callovian age. 
MATERIAL. Numerous specimens collected by the author and various members 
of Imperial College from the southern French Jura. 20 specimens in the author’s 
collection in British Museum (Nat. Hist.) nos. BB. 45690-45709. 
Description. External characters. The width is always greater than the length, 
resulting in a laterally suboval outline. The beak is very small and closely ad- 
pressed to the brachial valve ; no pedicle opening or deltidial plates are visible 
externally in the adult specimens. Beak ridges and interarea are both poorly 
developed. Adult specimens have between 25 and 30 ribs, as counted at the anterior 
