BRACHIOPODA. 
337 
SUPPLEMENTARY NOTE ON THE GENUS OBOLUS, VON EICHWALD. 
The preceding discussions of the inarticulate genera (ending on page 184) 
were received from the printer in March, 1890. Since that date an impor¬ 
tant contribution to our knowledge of the genus Obolus has been made by 
A. Mickwitz,* whose studies are based upon finely preserved material from 
Joafall, near Jegelecht, Esthonia. 
Students of the brachiopoda will appreciate the author’s statement that “this 
genus, notwithstanding the exceeding abundance of its shells in the upper layers 
of the Ungulitensandstein of our Cambrian formation, from Baltischport to the 
banks of the Sjas, and in spite of its early discovery, has been hitherto as good 
as unknown.” The details of the internal structure of both valves are worked 
out with such a degree of elaboration, that we can do no less than give in 
this place the author’s diagnosis of the genus and copies of his accompanying 
illustrations, observing that the genera Aulonotreta, Kutorga, and Schmidtia, 
Volborth, are here regarded as synonymous with Obolus : 
“ Shell nearly equivalve, equilateral, depressed or slightly convex; outline 
circular or somewhat elongate longitudinally or transversely, in some species 
subtriangular or elongate-quadrate. 
“ Shell-substance calcareo-corneous, structure laminated; surface lustrous, 
with concentric and radial striae varying to deeply incised transverse folds and 
radial ribs. Color of the shell dark greyish-blue to black; when in process of 
decomposition, whitish to dark brown-red. Anterior and lateral margins thin, 
sharply angled and fragile, lying in the plane of the greatly thickened cardinal 
margin. The cardinal area lies in the plane of the margins, in the larger valve 
being somewhat triangular on account of the elevation of the beak, and divided 
equally by the pedicle-groove ; in the smaller valve rounded at the apex, and 
in both striated parallel to the base, and grooved from apex to base by the 
*Vorlaufige Mittheilung iiber das genus Obolcs, Eirhwald : Melanges geologiques et paleontologiques 
tires du Bulletin de l’Academie Imperiale des Sciences de St. P^tersbourg, Tome I. (Read October 9th, 1890.) 
