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 

 ScJiizodus Bossicus, which in the ' Versteinerungen' is, incorrectly I think, assumed to 

 be the young of S. ScMotheimi. The fossil which Dr. Geinitz cites as an example 

 (vide pi. iii, fig. 33) supporting his view, I am disposed to consider, belongs either to 

 Schizodus rotundatus, Brown, or S. Bossicus. 



The triassic (?) MyopJioria cardissoides, Hartmann, represented in the ' Lethaea 

 Geognostica,' pi. xiii, fig. 9, has some resemblance to Schizodus ScMotheimi, 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. ScMotheimi somewhat sinuated in 

 the same part. 



Dr. Geinitz states that Schizodus ScMotheimi is a " characteristic shell in the upper 

 Zechstein, in which it is everywhere associated with Mytilus Hausmanni (query 

 M. septifer) ; also in the limestone of Paschkowitz near Miigeln, and of Frohburg in 

 Saxony, of Cosma, Sommeritz, Lehndorf, Zehma near Altenburg, and Roschiitz near 

 Gera ; in the Zechstein-Dolomite of Konitz, Gliicksbrunn, Salzungen, Ahlstedt near 

 Schleusingen, between AUendorf and Zizzendorf, and, according to Mielecki, in the 

 neighbourhood of Osterode (Katzenstein), Scharzfeld and Sachswerfen (near Miihlberg 

 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 wv\h 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, &c. The specimen 

 represented in PI. 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. 



