40 JURASSIC RHYNCHONELLIDS 
the ‘‘ Kimmeridgien of Wurttemberg ”’; 5 specimens in author’s collection from the 
“Malm epsilon ”’ of Franconia, in the British Museum (Nat. Hist.) nos. BB. 45750-54. 
DeEscripTION. External characters. The most striking feature of the species is 
the very marked trilobation shown by most specimens. The species appears to be 
unique, at least in the upper Jurassic, in that it shows a complete gradation of forms 
between trilobate symmetrical and bilobed strongly asymmetrical forms. Especially 
in the trilobate specimens, the brachial valve tends to be considerably the more 
inflated. 
The bifurcating ribs vary considerably in number and development ; generally 
their coarseness is inversely proportional to the number present. The concentric 
ornament, when present, consists of numerous fine growth lines. The beak is small 
and flanked by weakly developed beak-ridges ; the interarea is slightly incurved. 
The small pedicle opening is limited by conjunct deltidial plates. 
DIMENSIONS OF FIGURED SPECIMENS. 
length thickness width 
3:06 cm 2°25 cm 2°80 cm 
2°85 cm 2:05 cm 3°19 cm 
2°85 cm 1-63 cm 2-78 cm 
3°46 cm 2°55 cm 3°21 cm 
Internal characters. These were not investigated as the author’s collection 
contains only a very limited number of sufficiently well preserved specimens. 
DISTRIBUTION. The species appears to be restricted to the Swabian and Fran- 
conian Jura and the Schaffhausen area of Switzerland. 
OccURRENCE. The specimens collected by the author were obtained from well- 
bedded, fine-grained limestones ; they were the most abundant element in a fauna 
which also included ammonites and sponges. The fact that so few complete speci- 
mens were obtained is a result of the extremely hard, brittle nature of the host rock. 
Lacunosella sp. 
Specimens have been selected from material in the collection of the University of 
Tubingen in order to conform as nearly as possible to the specimens figured by 
Quenstedt (1858, 1871) as Terebratula lacunosa multiplicata (pl. 3, fig. 1) and T. 
lacunosa decorata (=Rhynchonella pseudodecorata of Rollier) (pl. 1, fig. 13). The 
author has not personally collected material referable to this species and as there is 
only a very limited amount available at Tiibingen, it has not been possible to give 
full descriptions. ‘“‘ Rhynchonella’’ pseudodecorata is of particular interest as it has 
been selected by Makridin (1955) as the type of his genus Jsjywminelina (=Isjumin- 
ella). As this species seems to be externally a typical member of Lacunosella, it is 
considered that Makridin probably misidentified his material as his description of 
its internal structures excludes it from that genus. 
Also figured is a specimen of L. selliformis (Lewinski) (pl. 2, fig. 4) from the 
Oxfordian of Poland and a specimen of L. tvilobataeformis Wisniewska (pl. 3, fig. 2). 
The latter is strongly homoeomorphic with Somalirhynchia moeschi and these two 
species appear to have been frequently confused in the past. 
