Diagnoza

The ne elements robust , with almost flat surfaces along the posterior ex ternalridge .
Mature elements prominently costate, the tr element usually bear five inner ribs (even in some juveniles). All the elements hyaline with rudimentary white matter .

Porównanie

The apparatus of D. robustus is of the same organization as that of D. arCII atus. Th e
only difference consists in the orn am entati on of the inner margin s of mature elements. Th ere are
populations transitional between these two species but the evolutio nary re lations hips between them
are far from being clarified. They probabl y formed a network of all op atri c, independently ev olv ing
lineages that occasionally int erbred unt il a complete separa tion of the lineages at an unknown level
of the Llan virn, when along with the D. robustus linea ge another line, lead ing from D. arcuat us to D.
santacru censis sp. n. was establishe d. Ju venile eleme nts of these spec ies are hardl y distinct morphologically.
In con sequ en ce of a high developmental and population va ria bility it is also not always
possible to separate som e morphologically close e leme nt types within the symme try transition se ries .

Autekologia

Występowanie geograficzne

Th e species appea rs in the M6jcza limestone at the di scon tinuity surface and
continues as high above as to 1.8 m above the bentonite (A . tvaerensislsup erbu s tran sition zo ne) . Ra re,
spec ifica lly unidentifiable eleme nts of Drepan odus occur spo radically even higher in the section.

Zasięg czasowy

Materiały muzealne

Literatura