73 



left one (fig. 6) cappeared (o possess a deep furrow as is the case 

 with Primitla Tol II. 



This, I think, shows sufficiently that Jones' orientation of the 

 valves of Bei/richia tiihercidata is the correct one. 



As further result of my investigation I may tell that the dorsal 

 edge of the right valve of Be>/rlc/ii<i tabercidata has a less deep 

 fnrrow, in which the sharp dorsal edge of the left valve lies. 



A more or less identical structure of the edges was also found in 

 Beyrichia Jonesti Boll var. dauata Kolmodln (17, p. 15), of which 



Fig. 7. 

 Transverse section of the entire 

 carapace of Beyrichia Jonesii Boll 

 var, clavala Kolmodin through the 

 part where the muscle impression is 

 undoubtedly located, anterior view. 

 X2Ü. 



Fig. 8. 



Part of the last figure magnified 

 four times. 



1 possess entire carapaces originating from the clay of Mulde in 

 Gotland (fig. 7 and 8). Here, however, the dorsal edge of the left 

 valve is rounded off. 



LITERATURE. 



1. Zittel, K, A. von. — Grundzüge der Palaeoniologie. (Palaeozoologie) 

 I Ahteilung Invertebrata, 3e Aufi. Miinchen u. Berlin, 1910. 



2. Kayser, E. — Lehrbiich der geologischen Formationskunde . 4e Aufl., 

 Stuttgart, 1911. 



3. BucH, L. VON. — " Ueber die Silification organischer Karper nebst einigen 

 anderen Bemerkungen ilber wenig bekannte Versteinerungen". Abhandl. d. 

 Königl. Akad. d. Wissensch. zu Berlin, 1828. 



4. Klöden, K F. — "Die Versteinerungen der Mark Brandenburg''. 

 Berlin, 1834. 



5. BuRMEisTER, H. - ■ "Die Organisation der Trilobiten'\ Berlin, 1843. 



6. Beyrich. — "Ueber einige böhmische Trilobiten'\ Berlin, 1845. 



7. M<^GoY, F. — A synopsis of Silurian fossils of Ireland". Dublin, 1846. 



