THE SHELL-LIMESTONE OF DURHAM. 161 



Gytherella nuciformis, Reuss. " Jahresb. Wetter. 



Geo. 1854," p. 68, fig. 9. 

 Cytherella nuciformis^ Richter. " Zeitscli. Dcut. 

 Geol. Ges." vol. vii., p. 529, pi. 26, figs. 8, 9. 

 Carapace oblong-oval, smooth, convex; dorsal and ventral 

 borders elliptical ; extremities rounded; anterior depressed, 

 ratlier narrower than the posterior] dorsal aspect com- 

 pressed, ovate; anterior oval. 

 From Byers' Quarry. Rather rare. 



Professor Reuss and Dr. Richter have met with this species 

 in the German Zechstein. 



This little species has a somewhat similar form to that of 

 Ci/therella Muensteri (Roemer sp.) of the Chalk and the Tertiary 

 beds. See "Jones' Monog. Tert. Entom.," p. 56. Forms of 

 carapace not very dissimilar to G. inornata and C. nuciformis oc- 

 cur with other Cytlieres in the carboniferous limestone of Kil- 

 bride, near Glasgow. 



8. C. {Bairdid) plebeia,* Reuss. PI. XL, fig. 8. 



Cytliere (Bairdia) curta, Jones (not M'Coy), in 



" King's Monog. Perm. Foss," p. 61. 

 Bairdia p)leheia^ ^QW^^. " Jahresb. Wetter. Gesell. 



1854," p. 67, fig. 5a, U. 



Cytliere (BaijxIiaJpIeheiay.K.irk'by. See above, p. 141. 



The specimen here figured is from Byers' Quarry, and has 



its carapace well preserved. It presents the usual form of the 



typical B. pleheia, with its well rounded antero-ventral border. 



It was not figured in the " Monog. Perm. Foss." 



Specimens of Bawdice (B. p)lebeia and its varieties) are not 

 uncommon at Humbleton and Byers' Quarry; but at the latter 

 place, especially, they are very imperfectly preserved. 



9. 0. {Bairdia) vh^^^ik, Reuss. Var. brevicauda. PL XL, figs, 



9a, 9^*, 9c. 



* Dr. Richter has figured and described some varieties of B. pleheia ("Zeitsch. ,Deut. 

 Geol. Ges.," vol. vii., pi. 26, figs. 10-15), under the name of Bairdia drupacea, B. Geinitzi- 

 ana, and B. curta. Dr. Richter himself has determined that the two former are varieties 

 of the last, which ia the synonym for B. pleheia, and which we now wish to withdraw. 



vol. IV. PT. II. V 



