FROM NORTHWESTERN EUROPE 71 
has not been satisfactorily observed. The test is evenly covered with bifurcating, 
spine-bearing ribs which are quite coarse, as compared with other species in the 
genus. A few growth lamellae are frequently present but growth lines have only 
been observed on one specimen. The anterior commissure has a characteristic low 
uniplication. 
DIMENSIONS OF FIGURED SPECIMENS. 
length thickness width 
I-70 cm I'00 cm 2°00 cm 
1°53 cm 0-93 cm 1-67 cm 
I-33 cm 0-70 cm 1°43 cm 
Internal characters. The specimen sectioned, which appeared to be of typical 
preservation for the locality, was very badly recrystallized and with the shell almost 
completely missing. The effect of this has been to obliterate the fine structure 
together with the crura which were rapidly lost in a mosaic of crystalline calcite ; 
the predominant lack of fine external ornament may also be a result of the poor 
preservation. 
Pedicle valve. Slender, slightly diverging dental lamellae are present and bound 
a subquadrate delthyrial cavity. The teeth are large with distinctly flattened bases. 
Brachial valve. The socket floors are very unusual in that they come to lie in 
a position sub-parallel to the plane of articulation. Both inner and outer socket 
ridges are well developed. 
DIsTRIBUTION. The species is only recorded from the type locality. 
OccuURRENCE. In his original remarks, Rothpletz described it as occurring fairly 
abundantly in a “‘ Brachiopoden-Lumachelle ” together with numerous molluscs. 
Remarks. The species differs from A. myriacantha, as figured by Deslongchamps 
(1859), in being larger, having a uniplication in the anterior commissure and in having 
much coarser ribs on which the spine bases are more sparsely distributed. The small 
disjunct deltidial plates figured by Deslongchamps have not been observed in A. 
(Acanthorhynchia) vilsensis. 
A. (Acanthorhynchia) sp. 
(Pl. 7, figs. Io-11, text-fig. 25 (bottom)) 
MATERIAL. 4 specimens including B.M. BB.44168, BB.44169. 
REMARKS. The material was collected from the thin bedded Oignon Limestone* 
(Ager and Evamy, 1963) near Colomieu (Ain). Both externally and internally, the 
species shows considerable resemblance to A. (Acanthorhynchia) spinulosa ; how- 
ever, the difference in stratigraphical horizon and the variability shown by the 
limited material available suggests that the species should be regarded as being 
derived from the former rather than conspecific with it. The largest specimen 
collected resembles one of the forms in the Orbigny Collection labelled Hemithiris 
senticosa. 
* Oignon Limestone is of Upper Kimmeridgian age. 
