NOTES ON THE BRITISH JURASSIC BRA.CHIOPODA. 37 



Bhynchonella, and even then the task is not infreqnentlj 

 verj difficult. 



The geographical distribution of the Rhynchonellas is very 

 interesting. Species found in one district may be altogether 

 absent in another. Even in the same bed of rock a certain 

 species may be found in one point in great numbers, while 

 at a distance of a few yards away it may be quite rare or 

 altogether absent. Many species were very prolific during 

 the Jurassic epoch, others such as B. ivrightii, egretta, fallax, 

 dorsetensis, dundriensts, and a few more are extremely 

 rare. 



The type of B. dundrie^isis, from the Inferior Oolite of 

 Dundry, is located in our museum (23), while the types of 

 the following Rhynchonellje are carefully preserved in the 

 Bath Museum : — 



B. bouchardii, Dav., from the Upper Lias of Ilminster. 



B. (?) coronata^ Moore, ,, „ ,, ,, 



B. 7noorei, Dav., ,, „ „ „ 



B. piigmea, Morris, 



B. sub- cone i7i7ia, Dav., ,, Middle ,, ,, 



B. (?) lopensis, Moore, Inferior Oolite, Lopen, near Ilminster. 

 Also described specimens of 



B. furcillata, Theodori, Middle Lias of Ilminster. 

 B. serrata, Sow., ,, ,, Moolham. 



B. tetrahedra, Sow., „ „ Ilminster. 



ACANTHOTHYRIS, d'Orbigny, 1850. 



Etym. — aKavOa, a spine; Ovpis, a small opening. 

 Syn. — Bhynchonella, Davidson, 1884. 



A. {Bhyn.) spinosa, Linn. A shell of the upper beds of 

 the Inferior Oolite is the type of this genus. 



The external surface of the valves of Acanthothyn's is 



