FROM NORTHWESTERN EUROPE 29 
Internal characters. Pedicle valve. The most striking features are the massive 
shell and the very reduced dental lamellae ; lateral cavities are hardly developed. 
Pedicle collars were not present in all the species sectioned but as it seems probable 
that these are only developed in the adult specimens, their absence may be the result 
of sectioning slightly immature material. The teeth are strong and frequently show 
some degree of crenulation ; lateral denticulae are usually present. In fully adult 
specimens the muscle attachment areas can be clearly seen as quite deep depressions 
in the shell. 
Brachial valve. There is no septalium and the median septum, if present, is very 
much reduced. The hinge plates are divided and, almost as soon as the cavity of 
the brachial valve is exposed during serial sectioning, the long falcifer crura can 
be seen hanging down from them into the brachial valve. The presence of falcifer 
crura distinguishes Lacwnosella from all other Upper Jurassic genera. Inner and 
outer socket ridges are both well-developed. 
SpEcIES. The following nominal species are attributed to the genus : 
. amstettensis (Fraas) (1858, pp. 107-8) 
. avolica (Oppel) (1865, p. 312) 
. blanowicensis Wisniewska (1932, pp. 40-1, pl. iu, figs. 1-5) 
. cracoviensis (Quenstedt) (1871, p. 136, pl. xl, fig. 43) 
. dilatata (Rollier) (1917, p. 134) 
. kozlowskw Wisniewska, (1932, pp. 54-55, Ppl. v, figs. 1-7) 
. monsalvensis (Gilliéron) (1873, p. 244, pl. x, figs. 11-12) 
. multiplicata (Zieten) (1832, p. 55, pl. xli, fig. 5) 
. polita (Quenstedt) (1871, p. 126, pl. xxxix, fig. 106) 
. prosimilis (Rollier) (1917, p. 174) 
. pseudodecorata (Rollier) (1917, p. 139) 
. selluformis (Lewinski) (1908, p. 437, pl. xxii, fig. 8-11) 
. stlicea (Quenstedt) (1871, p. 129, pl. xxxix, fig. 107) 
. slemivadzku (Wisniewska) (1932, pp. 48-49, pl. iii, figs. 21, 22) 
. sparsicosta (Quenstedt) (1858, pp. 633-34, pl. Ixxviii, figs. 12-22) 
. subsimilis (Schlotheim) (1820, p. 264) 
. trilobata (Zieten) (1832, p. 56, pl. xlii, fig. 3) 
. trilobataefornis Wisniewska (1932, pp. 46-48, pl. iv, figs. 1-11) 
vaga sp. nov. 
. visulica (Oppel) (1866, p. 295). 
Sielalalelelalolalalelelslaialalelelals: 
DISTRIBUTION. The genus has been recorded throughout the French, German 
and Swiss Jura, from Poland and from Stramberk, Czechoslovakia. 
OccURRENCE. With the exception of the occurrence of L. vaga on the Col du 
Chat (Savoie) the genus is always associated with sponges. This association has 
been commented on by Quenstedt (1871), Ager and Evamy (1963) and Ager (19652). 
The genus is most abundant and varied in the Swabian and Franconian Jura where 
it occurs in the bedded limestones associated with the sponge reefs. 
The massive shell and consistent presence of a pedicle opening, presumably 
indicating a functional pedicle, seem to be adaptations to a high energy environment 
