30 JURASSIC RHYNCHONELLIDS 
around the reefs. The persistent occurrence of sponges with Lacunosella is so 
striking that it suggests that the genus was in some way dependent on them. 
Several times while collecting material, the author found specimens of Lacunosella 
actually in contact with sponges. While this may have been coincidence, it could 
also have been the result of the rhynchonellids actually having been attached to the 
sponges. It is difficult to see what particular benefit this would have been and why 
Lacunosella should have restricted itself to attachment on that particular ‘ host ’. 
At the locality mentioned above where sponges are not present, L. vaga was obtained 
from bedded limestones associated with “‘ reef ’’ limestones. 
Lacunosella arolica (Oppel) 
(Pl. 1, figs. 11-12, text-figs. 12-13) 
1864 Rhynchonella lacunosa (Schlotheim); Heer: 137, fig. 87. 
1865 Rhynchonella Arolica Oppel: 312. 
1866 Rhynchonella Arolica Oppel; Oppel and Waagen: 294. 
1867 Ehynchonella Avolica Oppel; Moesch: 310-311, pl. 7, fig. 9. 
1871 Tevebratula lacunosa Arolica Quenstedt; 127, pl. 39, figs. 95-96. 
1885 Tevebratula lacunosa Arolica Quenstedt: 693, pl. 53, fig. 60. 
1890 Rhynchonella lacunosa (Quenstedt) var. Avolica Oppel; Haas: 48-50, pl. 3, figs. 1-22, pl. 
4, figs. I-5. 
1917. Rhynchonella Avolica Oppel; Rollier: 134. 
1918 Stolmorhynchia avolica (Oppel); Buckman: 46. 
1932 Lacunosella arolica (Oppel); Wisniewska: 33-38, pl. 2, figs. 1-18. 
EMENDED DIAGNOSIS. Medium to large sized, relatively flattened Lacunosella ; 
outline subpentagonal ; 9g—11 low, subangular ribs; crura falcifer. 
STRATIGRAPHICAL RANGE. Oxfordian—upper cordatum and transversarium zones. 
TYPE SPECIMEN. In his original description of the species Oppel cited the figure 
in Heer (1864) listed above. 
MATERIAL. 16 specimens collected by the author from the southern French 
Jura in the British Museum (Nat. Hist.) nos. BB. 45630-45639, BB. 45678-45681 ; 
43 specimens collected by Dr. Enay from the central French Jura ; 12 specimens 
from the “ Birmensdorfer-Schichten’’ of Switzerland donated by the Natur- 
historisches Museum, Basel. 
DescripTiIon. External characters. The shell is biconvex with the brachial 
valve slightly the more inflated ; however, both valves are relatively flattened com- 
pared with other species of the genus. The beak is small and suberect ; beak 
ridges and interarea are hardly differentiated. The small, submesothyridid pedicle 
opening is flanked by conjunct deltidial plates. 
The radial ornament consists of about eleven low, subangular ribs, the majority of 
which originate at the umbones although bifurcation is not uncommon. Numerous 
fine growth lamellae are characteristically present. The anterior commissure has a 
well-marked uniplication which usually carries three or four ribs ; however, it is 
often distorted to some degree by asymmetrical development. 
