LAMELLIBRANCHIATA. 101 



ExoGYRA CONICA, Sby., vars. including (Plate iv. fig. 3, 



a, b, c) 



Chama conica, Sby., 1812. Min. Con. pi. 26, fig. 3. 

 Exogyra conica, Sby., Min. Con. t. 605, figs. 1 — 3. 

 „ undata, Sby., Min. Con. t. 605, figs. 3, 4. 

 „ spiralis, Roemer, 1839. N. Ool. p. 65 {pars). 

 „ undata, „ 1841. Nordd. Kreid, p. 47, No. 7. 

 Ostea Tomheckiana, d'Orb., Terr. Cret. p. 701, pi. 467, figs. 

 4—6. 

 „ conica, „ „ p. 726, pi. 478, figs. 



5—8. 



Our Upware forms are usually known as Exogyra Tomheckiana 

 in England and France, but they are called E. spiralis in the Ger- 

 man Museums. Prof. Morris and Mr Blake record E. spiralis as 

 an oolitic species (Portland Oolite and Coral Rag), and Roemer in 

 his original description gives both the Corallien and the Elligser- 

 brink beds (Neocomian), for its horizons. The Jurassic and 

 Cretaceous shells do indeed closely correspond, and they all belong 

 to the same group. Exogyra nana is especially near to the 

 variety spiralis, and others very nearly resemble even E. virgula, 

 some of the specimens having been mistaken for this latter species 

 and recorded as such in the published lists of Potton Shells. 



Three well-marked types of this species occur at Brickhill, 

 namely : 



(1) Exogyra conica, Sby., i^ar. Tomheckiana^ d'Orb. This is 

 the true Ostrea Tomheckiana, a small smooth species, with crenu- 

 lated lip. 



(2) Exogyra conica, Sby., var. spiralis, Roemer. A variety 

 having its upper valve ornamented with regular and distinct 

 imbrications; and 



(3) a striated variety. 



Localities. Upware, Potton, Brickhill, Farringdon, Black- 

 down. 

 N. Europe. Haverlah, Gevensleben; Schoeppenstedt, Hils 



Conglomerat. 

 S. Europe. Mont Sal^ve, Perte du Rhone, etc. 



I 



