38 JURASSIC RHYNCHONELLIDS 
inflated than the pedicle. The most frequent number of ribs developed is seven, of 
which three lie in the fold ; these latter ribs are coarse and subangular, contrasting 
with the lower more rounded ones occurring laterally. There is a posterior smooth 
area, as the ribs do not originate from the umbones ; the central ribs are, however, 
developed much further posteriorly than the lateral ones. The ribs are mostly 
simple. Growth lamellae are usually present but are very variably developed. 
The beak is small and suberect. A small, submesothyridid pedicle opening is 
flanked by small, conjunct deltidial plates. The interarea and beak ridges are only 
very poorly differentiated. 
DIMENSIONS OF FIGURED SPECIMENS. 
length thickness width 
I-61 cm 1:03 cm 1°73 cm 
1:98 cm 1:93 cm 2°23 cm 
Internal characters. Pedicle valve. There is a well-developed pedicle collar. 
The shell is massive and the dental lamellae are only poorly developed so that lateral 
cavities are hardly present. The delthyrial cavity is subquadrate and ventrally the 
depressions of the muscle attachment areas can be clearly seen. The teeth are 
strong and lateral denticulae are present. 
Brachial valve. Inner and outer socket ridges are both well-developed. Other 
features are as described for the genus. 
DISTRIBUTION. The species ranges from the northern Franconian Jura through 
the Swabian Jura to the Schaffhausen area of Switzerland. 
OccuRRENCE. The author has only collected the species from one locality, 
namely Barrenberg in Franconia. The exposure there was not very good but 
appeared to represent perireefal limestones which had been broken up and the 
resulting angular blocks recemented. L. sparsicosta was the commonest element in 
a rich fauna which also included sponges, ammonites, L. cracoviensis, Monticlarella 
strioplicata ‘normal’ terebratulids and the sulcate terebratulid Nucleolata. 
Lacunosella trilobata (Zieten) 
(Pl. 3, figs. 3-6) 
1832 Tevebvatula trilobata Minster; Zieten: 56, pl. 42, fig. 3. 
1832 Terebratula inaequilatera Goldfuss; Zieten: 56, pl. 42, fig. 4. 
1845 Tevebvatula trilobata Zyszner: pl. 5, figs. 1-5. 
1870 Rhynchonella trilobata Moesch: 145, pl. 14, fig. 33. 
1871 Terebratula trilobata Quenstedt: 134-36, pl. 40, figs. 35-39, ?figs. 40-44. 
1890 Rhynchonella trilobata (Zieten); Haas: 55-58, pl. 7, figs. 3-6. 
1917 Rhynchonella trilobata (Zieten); Rollier: 175. 
1917. Rhynchonella inaequilatera (Zieten); Rollier: 176. 
1918 Stolmorhynchia trilobata (Zieten); Buckman: 46. 
1932 Lacunosella trilobata (Zieten); Wisniewska: 32. 
EMENDED DIAGNOSIS. Medium-sized, elongated Lacunosella ; very strongly 
trilobate or asymmetrical ; 17-24 rather shallow, subangular ribs of which 6-9 lie 
on the fold. 
