112 



and vary considerably in thickness (maximum is about 1 1 mm.). 

 Their surface seems to have been smooth. — As all that 1 

 have seen of the shells are a few insignificant casts, a closer 

 determination is impossible. 



The Coeloma-bed: Many specimens. 



Besides the above mentioned lamelHbranchs I have seen a 

 few other species from the Cyrena-bed, which however are so 

 imperfect, that even the determination of the genus is impos- 

 sible. One has some resemblance to certain species of Corbula. 



B. Gastropoda. 



14. Natica sp. 



Plate IV, fig. 3. 



Some specimens of a Gastropod certainly belong to the 

 genus Natica. As it is impossible to separate the shell from 

 the sandstone only the casts are available for examination, and 

 a more exact determination is therefore unfortunately impossible. 



The Cyrena-bed: 4 specimens. 



15. Aporrhais speciosa v. Schlotheim sp. 

 Plate IV, figs. 4—5. 



1820. Strombites speciosus v. Schlote, sp.; Petrefactenkunde p. 155. 



1854. Aporrhais speciosa — - Beyrich, Conch, des nord- 



deutsch. Tertiärgeb. p. 170; pi. 11, fig. 1—6. 



1867. Aporrhais speciosa Schlote.; v. Koenen, Das marine Mittelolig. 

 Norddeutschlands, p. 14. 



Four specimens from the Cyrena-bed, one rather perfect, 

 the others casts, seem to belong to this species. This is at 

 any rate undoubtedly the case with the specimen which is in the 

 best state of preservation, since it shows distinctly the numerous 

 sloping transverse ribs, and here and there parts of the spiral 



