FROM NORTHWESTERN EUROPE 65 
hynchia s.s. lived in fairly high energy environments. The specimens of Echinir- 
hynchia collected from the French Jura came from very fine-grained sediments, 
either clays or calclutites, while the material recorded from Germany is also either 
from clays e.g. Terebratula senticosa impressae Quenstedt, or from the sponge reef 
facies e.g. A. (Echinirhynchia) senticosa (Schlotheim). The occurrence of the sub- 
genus in these two markedly different facies may possibly indicate that its mode of 
life was planktonic or that it lived attached to floating weed ; this hypothesis was 
suggested by Ager (19652). 
Sub-genus ACANTHORHYNCHIA s.s. 
TYPE SPECIES. Acanthothyris panacanthina Buckman and Walker. 
Diacnosis. Medium to large species of Acanthorhynchia with a transversely oval 
to subrounded outline ; either equally biconvex or with a more inflated brachial 
valve ; deltidial plates and dental lamellae may be present. 
STRATIGRAPHICAL RANGE. Upper Bajocian—Upper Volgian/Neocomian. 
DIsTRIBUTION. The sub-genus has a wide range both geographically and chrono- 
logically ; however, the consistent external and internal features of the included 
species suggest a continuous evolutionary lineage. The extent of the geographical 
range is given under the species description. Apart from the species described A. 
(Acanthorhynchia) multistriata (Kitchin) is recorded from the “ Oomia Group” of 
the Kutch and A. (Acanthorhynchia) rogans (Szajnocha) occurs in the “ Balin Oolite ”’ 
of Poland. 
A. (Acanthorhynchia) panacanathina (Buckman and Walker) 
(Pl. 6, figs. 5-7, text-fig. 24) 
1851 &hynchonella senticosa (Buch); Davidson: 73-74, pl. 15, fig. 21. 
1878 Rhynchonella senticosa (Buch); Davidson: 223. 
1878 Rhynchonella senticosa (Buch); Davidson: 85, pl. 4, fig. 20. 
1882 Rhynchonella senticosa (Buch); Buckman: 41-42. 
1889 <Acanthothyris panacanathina Buckman and Walker: 53—54.[ =A. Davidsoni Rollier 1917]. 
1918 <Acanthorhynchia panacanathina Buckman and Walker; Buckman: 69-70, pl. 19, fig. 23. 
[=A. Davidsoni Rollier 1917}. 
EMENDED DIAGNOSIS. Large Acanthorhynchia which ranges in size up to 3:05 cm 
long, 2-20 cm thick and 3:53 cm wide. Biconvex and transversely suboval in out- 
line ; beak suberect ; deltidial plates narrow, trigonal and disjunct ; anterior 
commissure sinuate ; crura calcarifer. 
STRATIGRAPHICAL RANGE. Bajocian—probably restricted to the parkinsoni zone. 
TYPE SPECIMEN. In their synonymy Buckman and Walker (1889) mention the 
specimen figured by Davidson (1851) on pl. 15, fig. 21 and it seems reasonable to 
take this as the type of the species. B 12082 (B.M. (N.H.)) 
DEscripTION. External characters. This is the largest known species of Acan- 
thorhynchia. ‘The test is covered with fine ribs ; Buckman and Walker cite a speci- 
men as having about a hundred ribs on each valve, with forty spines on each rib. 
This statement seems to be essentially correct, although the fineness of the features 
concerned is such as to preclude accurate counting except on well preserved and 
