THE SHELL-LIMESTONE OF DURHAM. 159 



ventral borders straight, slightly incurved ; extremities 

 sub-acute, suddenly depressed; the anterior slightly nar- 

 rower than the posterior; dorsal aspect elongate oval, 

 compressed at the ends ; anterior sub-ovate. 



This was most probably a true Cytliere. 



From Byers' Quarry and Humbleton. Rare. 



2. C. ELONGATA, Munster.{l) PI. XI., fig. 2. 



Cythere elongata, Mlinster. " Jahrbuch f. Min. 1836," 

 p. 65, no. 19; Jones, in " King's Monog. Perm. 

 Foss.," p. 62, pi. 18, fig. 5. 

 Carapaoe bean-shaped, smooth, convex ; dorsal and ventral 

 borders slightly incurved at the middle ; extremities 

 rounded, the anterior more obliquely than the posterior. 

 Munster's description of C. elongata (from the Bergkalk of 

 Regnitzlosau), is very succinct; but, as far it goes, is applicable 

 to this species. A very similar form {Cytliere proper) lives in 

 the Mediterranean. 



A single specimen, imbedded in a fragment of magnesian 

 limestone, dredged up near the Dogger Bank. 



3. C. KuTORGiANA, Joues. PL XI., figs. 3«, 3Z>. Jones, in 



<' King's Monog. Perm. Foss.," p. 62, pi. 18, fig. 6. 

 Carapace somewhat bean-shaped, or resembling a peach- 

 stone, convex; dorsal border elliptical ; its contact mar- 

 gin thickened and bearing traces of hinge ; ventral sinu- 

 ous ; anterior extremity obliquely rounded ; posterior acute. 

 Fig. 35 represents a larger and relatively narrower individual 

 than fig. 3a, which was the specimen figured in the " Monog. 

 Perm. Foss." This form of carapace is common among the 

 group of Cythere proper. 



Not common at Byers' Quarry. 



4. C. Geinitziana Jones. PI. XI., figs. 4a, 45, Ac. " King's 



Monog. Perm. Foss.," p. 62, pi. 6, fig. 46; pi. 18, 

 figs. 4a, 45, Ac. 

 Carapace elongate reniform, convex, smooth, slightly punc- 

 tuated towards the anterior extremity ; rounded anteriorly. 



