28 JURASSIC RHYNCHONELLIDS 
Brachial valve. A long, well developed median ridge is present. The hinge plates 
are flat. Both the inner and outer socket ridges are clearly differentiated. 
DISTRIBUTION. Apart from the Swabian and Franconian Jura and Poland, the 
only other records of the species are those of Jacob and Fallot (1913) from Mont 
Crussol and from Chomérac (Ardéche). A possible specimen of M. strioplicata was 
figured by Struckman (1878) from near Hanover. 
OccURRENCE. The species has been collected by the author from only two locali- 
ties, namely, at Lochengriindle in the Swabian Jura and at Barrenberg in Franconia. 
The former locality has been described in the remarks on the occurrence of M. 
striocincta. The latter locality is of ‘“‘ Malm gamma ”’ age and is again in the sponge 
reef facies. The fauna included many lacunosellids, terebratulids, small sponges, 
ammonites and occasional belemnites and echinoids, with M. stvioplicata one of the 
least abundant faunal elements. This locality is further described under Lacuno- 
sella sparsicosta. 
Family WELLERELLIDAE Likarev im Rzhonsnitskaya, 1956 
Subfamily LACUNOSELLINAE Smirnova, 1963 
Genus LACUNOSELLA Wisniewska, 1932 
1932 Lacunosella Wisniewska: 30-32. 
1960 Lacunosella Wisniewska; Makridin: 254. 
1965 Lacunosella Wisniewska; Ager: 608. 
TyPE SPECIES. Rhynchonella arolica Oppel, by original designation. 
EMENDED DIAGNOSIS. Medium to large rhynchonellids ; outline usually sub- 
pentagonal ; ribs bifurcate ; beak small; beak ridges and interarea poorly 
developed ; shell massive ; very reduced dental lamellae ; crura falcifer. 
STRATIGRAPHICAL RANGE. Oxfordian—Kimmeridgian—Lower Volgian ; upper 
cordatum to Gravesta spp. zones. 
DescripTION. External characters. The shell is either equally biconvex or with 
the brachial valve the more inflated. The test frequently has a characteristic and 
distinctive translucent, pearly appearance. Although the outline is usually sub- 
pentagonal, it may be strongly trilobate as in L. ¢trilobata. The genus is usually 
symmetrically developed with a uniplication in the anterior commissure, however, 
this feature is frequently displaced by asymmetrical development and completely 
asymmetrical, bilobed variants are produced by L. tvilobata. 
The ribbing is variable and in different species the rib count at the anterior com- 
missure varies between five and twenty-five. One of the most distinctive external 
features is that while not all the ribs bifurcate, this character is invariably shown by 
some of them. 
A small suberect beak is present, as are beak ridges and an interarea although both 
the latter are only poorly developed. The submesothyridid pedicle opening is 
flanked by conjunct deltidial plates. Concentric ornament, which is neither strongly 
developed nor consistently present, comprises fine growth lines and weakly developed 
growth lamellae. 
