192 PERMIAN FOSSILS. 
the anterior margin; - truncated obliquely at the posterior extremity; flatly convex 
at the ventral margin; and rather sloping behind the umbones. 
Dr. Geinitz states that young specimens are not so elongated posteriorly, nor so 
inequilateral as old ones: this is precisely the case with specimens found in Durham ; 
but I have never seen any so decidedly rounded marginally, or so nearly equilateral, as 
Schizodus Rossicus, which in the ‘ Verstemerungen’ is, incorrectly I think, assumed to 
be the young of 8. Schlotheim:. The fossil which Dr. Geinitz cites as an example 
(vide pl. ii, fig. 33) supporting his view, I am disposed to consider, belongs either to 
Schizodus rotundatus, Brown, or S. Rossicus. ; 
The triassic(?) JJZyophoria cardissoides, Hartmann, represented in the ‘ Lethza 
Geognostica,’ pl. xiii, fig. 9, has some resemblance to Schizodus Schlotheimi, particularly 
the specimen represented in Plate XV, fig. 32, which I have, with some hesitation, 
identified with the Geinitzian species. The specimen cited, which is imperfect at the 
dorsal margin, and therefore represented with too great a slope at this part, has a 
portion of the shell remaining, which is thick and strongly laminated: the posterior 
oblique ridge is rather prominent ; and immediately in front of and parallel to it, there 
is a shallow furrow, which has produced a slight sinus at the posterio-ventral margin. 
I have seen undoubted, but smaller, specimens of S. Schlothermi somewhat sinuated in 
the same part. 
Dr. Geinitz states that Schizodus Schlotheimi is a “ characteristic shell in the upper 
Zechstem, in which it is everywhere associated with Mytilus Hausmann (query 
M. septifer) ; also in the limestone of Paschkowitz near Migeln, and of Frohburg in 
Saxony, of Cosma, Sommeritz, Lehndorf, Zehma near Altenburg, and Roschiitz near 
Gera; in the Zechstein-Dolomite of Konitz, Glicksbrunn, Salzungen, Ahlstedt near 
Schleusingen, between Allendorf and Zizzendorf, and, according to Mielecki, in the 
neighbourhood of Osterode (Katzenstein), Scharzfeld and Sachswerfen (near Mihlberg 
in the white Dolomite) in the Hartz.” In the county of Durham it is a characteristic 
fossil in the uppermost beds of the Permian series, and associated with Mytilus septifer: 
it has occurred to me in these beds at Roker, Suter-point Bay, Marsden, Cleadon Hills, 
Byers’s Quarry, at the site of the new docks opposite Sunderland, and at the South 
end of Black Hall Rocks. I have never found it in the Shell-limestone of Humbleton 
Hill, or any other locality, associated with Schizodus truncatus, &e. The specimen 
represented in Pl. XV, fig. 32, was found by Mr. Binney at Newtown near Manchester : 
I have seen other specimens from the same locality. A fine specimen in the York 
Museum was collected at Stapleton Park. 
