FROM NORTHWESTERN EUROPE 63 
The evidence of the lithology is such as to suggest a rather high energy environ- 
ment. Given that the latter deduction is correct, it seems to the author that the 
spines would have been a useful anchoring device and it is considered that Rudwick 
(1964) under-estimated this function in proposing a sensory role for them. 
Remarks. A plaster cast of the specimen from the Orbigny collection figured by 
Thevenin (1910) has been examined, through the kindness of Dr. Fischer of the 
Jardin des Plantes (Musée d’histoire Naturelle), and externally this closely resembles 
the material collected from the southern French Jura. However, a conspecific 
identification has not been given as no topotype material has been sectioned and 
hence no comparison of the internal structures has been possible. The main 
difference between the Orbigny specimen and those described from the Jura lies in 
the rib count ; that of the former being 20 while that of the latter is between 25 and 
30. As the other two specimens of A. costata in the Orbigny collection are only 
poorly preserved (Dr. D. V. Ager, personal communication 1965), it is not considered 
reasonable to separate the Jura form as a new species merely on the basis of the 
slight difference in the number of ribs without an investigation of topotype material 
of the Orbigny species to ascertain its variation and internal structure. 
Genus ACANTHORHYNCHIA Buckman 
1914 Acanthorhynchia Buckman: 2, (nomen nudem). 
1918 Acanthorhynchia Buckman: 69. 
1960 Acanthorhynchia Buckman; Makridin: 256. 
1965b Acanthorhynchia Buckman: Ager: H611. 
TyPE SPECIES. Acanthothyris panacanthina Buckman and Walker, by original 
designation. 
EMENDED DIAGNOSIS. Small to medium sized rhynchonellids ; transversely oval 
or sub-triangular in outline ; thin test covered by numerous fine spine-covered ribs ; 
anterior commissure rectimarginate or with slight uniplication ; deltidial plates 
absent, or reduced and disjunct ; crura calcarifer or radulifer. 
STRATIGRAPHICAL RANGE. Upper Bajocian—Upper Volgian/Neocomian. 
DeEscriPTIon. External characters. The genus contains a series of small to 
medium sized rhynchonellids. The smaller species tend to be subtriangular in out- 
line, equally biconvex and generally flatter, while the larger species are transversely 
oval in outline, more globose and with the brachial valve more inflated than the 
pedicle. 
The anterior commissure may have a slight uniplication in the larger forms, but in 
the smaller it is usually straight. The beak is relatively small and suberect or erect ; 
deltidial plates are absent in the smaller forms and of a reduced, disjunct variety in 
the larger. Beak ridges and interarea are never well developed. There are typically 
one or two well developed growth lamellae, but the finer growth lines have not been 
observed. The test is covered with many fine, bifurcating ribs, from the crests of 
which are developed the characteristic, numerous fine spines which project at a low 
angle. 
