FROM NORTHWESTERN EUROPE 79 
extended to Russia, as it appears from Makridin’s figures that some at least of his 
species of the genus Praecyclothyris should be attributed to Somalirhynchia. That 
the genus has not previously been recorded from Europe is probably the result of its 
name, which has possibly been taken by previous authors as implying a restricted 
geographical occurrence. 
Somalirhynchia sutherlandi (Davidson) 
(Pl. 7, figs. 12-16, text-fig. 29) 
1873 Rhynchonella Sutherlandi Davidson: 196, pl. 8, figs. 1-2. 
1878 Rhynchonella Sutherlandi Davidson; Davidson: 190-91, pl. 25, figs. 5-8. 
1917 Rhynchonella Sutherlandiae Davidson; Rollier: 172. 
1918 Rhynchonella Sutherlandi Davidson; Buckman: 51. 
EMENDED DIAGNOSIS. Medium to large sized Somalirhynchia ; 15-25 coarse, 
simple, angular ribs ; usually trilobate ; suberect beak, septalium present ; crura 
radulifer. 
STRATIGRAPHICAL RANGE. Kimmeridgian—probably restricted to the upper 
mutabilis and pseudomutabilis zones. 
TYPE SPECIMEN. Lectotype, here selected, the specimen figured by Davidson 
(1878), pl. 25, fig. 5). 
MATERIAL. 1g specimens from the collection of the Geological Survey of Scotland, 
together with the very limited material available at the B.M.(N.H.) nos. B. 29749, 
B. 29752, B. 22586, B. 29751, B. 29753. A recent attempt by the author to collect 
further material yielded a single fragmentary specimen. 
DESCRIPTION. External characters. The species is distinctive on account of the 
very large size attained by many individuals ; Davidson (1878) claimed it to be the 
largest Mesozoic rhynchonellid. The outline is subpentagonal and the shell is 
biconvex with the brachial valve the more inflated. It is generally trilobate but a 
few specimens have been observed displaying quite marked asymmetry. Width, 
according to Davidson, is always greater than length, and while this seems to be 
correct the crushed nature of much of the material makes this difficult to ascertain 
in more than a few cases. Plate 7 figures the best preserved material available. 
The strong, suberect beak is flanked by well defined beak ridges which limit the 
incurved interarea. A relatively small pedicle opening is present ; the deltidial 
plates, as seen in transverse section, are strongly conjunct. Fine, concentric growth 
lines have been observed on one specimen ; this may well reflect the poor preserva- 
tion rather than the genuine lack of such ornament on most specimens. 
DIMENSIONS OF FIGURED SPECIMEN. 
length thickness width 
2°67 cm 2°33 cm 3:16 cm 
Internal characters. The specimen sectioned was slightly crushed, resulting in 
dorso-ventral flattening of the shell. The outline of some of the internal features 
was partly distorted by pressure solution caused by the coarse, quartz matrix. 
